For loop in matlab

For loop in matlab DEFAULT

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Loop Control Statements

With loop control statements, you can repeatedly execute a block of code. There are two types of loops:

  • statements loop a specific number of times, and keep track of each iteration with an incrementing index variable.

    For example, preallocate a 10-element vector, and calculate five values:

    x = ones(1,10); for n = 2:6 x(n) = 2 * x(n - 1); end
  • statements loop as long as a condition remains true.

    For example, find the first integer for which is a 100-digit number:

    n = 1; nFactorial = 1; while nFactorial < 1e100 n = n + 1; nFactorial = nFactorial * n; end

Each loop requires the keyword.

It is a good idea to indent the loops for readability, especially when they are nested (that is, when one loop contains another loop):

A = zeros(5,100); for m = 1:5 for n = 1:100 A(m, n) = 1/(m + n - 1); end end

You can programmatically exit a loop using a statement, or skip to the next iteration of a loop using a statement. For example, count the number of lines in the help for the function (that is, all comment lines until a blank line):

fid = fopen('magic.m','r'); count = 0; while ~feof(fid) line = fgetl(fid); if isempty(line) break elseif ~strncmp(line,'%',1) continue end count = count + 1; end fprintf('%d lines in MAGIC help\n',count); fclose(fid);

Tip

If you inadvertently create an infinite loop (a loop that never ends on its own), stop execution of the loop by pressing Ctrl+C.

See Also

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Sours: https://www.mathworks.com/help/matlab/matlab_prog/loop-control-statements.html

while

Main Content

Syntax

while end

Description

example

evaluates an expression, and repeats the execution of a group of statements in a loop while the expression is true. An expression is true when its result is nonempty and contains only nonzero elements (logical or real numeric). Otherwise, the expression is false.

Examples

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Repeat Statements Until Expression Is False

Use a loop to calculate .

n = 10; f = n; while n > 1 n = n-1; f = f*n; end disp(['n! = ' num2str(f)])

Skip to Next Loop Iteration

Count the number of lines of code in the file . Skip blank lines and comments using a statement. skips the remaining instructions in the loop and begins the next iteration.

fid = fopen('magic.m','r'); count = 0; while ~feof(fid) line = fgetl(fid); if isempty(line) || strncmp(line,'%',1) || ~ischar(line) continueend count = count + 1; end count

Exit Loop Before Expression Is False

Sum a sequence of random numbers until the next random number is greater than an upper limit. Then, exit the loop using a statement.

limit = 0.8; s = 0; while 1 tmp = rand; if tmp > limit breakend s = s + tmp; end

More About

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Expression

An expression can include relational operators (such as or ) and logical operators (such as , , or ). Use the logical operators and to create compound expressions. MATLAB® evaluates compound expressions from left to right, adhering to operator precedence rules.

Within the conditional expression of a block, logical operators and behave as short-circuit operators. This behavior is the same as and , respectively. Since and consistently short-circuit in conditional expressions and statements, it is good practice to use and instead of and within the expression. For example,

x = 42; while exist('myfunction.m','file') && (myfunction(x) >= pi) disp('Expressions are true') breakend

The first part of the expression evaluates to false. Therefore, MATLAB does not need to evaluate the second part of the expression, which would result in an undefined function error.

Tips

  • If you inadvertently create an infinite loop (that is, a loop that never ends on its own), stop execution of the loop by pressing Ctrl+C.

  • If the conditional expression evaluates to a matrix, MATLAB evaluates the statements only if all elements in the matrix are true (nonzero). To execute statements if any element is true, wrap the expression in the function.

  • To programmatically exit the loop, use a statement. To skip the rest of the instructions in the loop and begin the next iteration, use a statement.

  • When nesting a number of statements, each statement requires an keyword.

  • The MATLAB loop is similar to a loop in other programming languages, such as C and C++. However, evaluates the conditional expression at the beginning of the loop rather than the end.

    do % Not valid MATLAB syntax statements while expression

    To mimic the behavior of a loop, set the initial condition of to and place the conditional expression inside the loop. For example, implement the loop above by using a MATLAB loop.

    while true statements if ~expression break end end

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Introduced before R2006a

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for

Main Content

Syntax

for = end

Description

example

executes a group of statements in a loop for a specified number of times. has one of the following forms:

  • : — Increment the variable from to by , and repeat execution of until is greater than .

  • :: — Increment by the value on each iteration, or decrements when is negative.

  • — Create a column vector, , from subsequent columns of array on each iteration. For example, on the first iteration, . The loop executes a maximum of times, where is the number of columns of , given by . The input can be of any MATLAB® data type, including a character vector, cell array, or struct.

Examples

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Assign Matrix Values

Create a Hilbert matrix of order 10.

s = 10; H = zeros(s); for c = 1:s for r = 1:s H(r,c) = 1/(r+c-1); endend

Decrement Values

Step by increments of , and display the values.

for v = 1.0:-0.2:0.0 disp(v) end
1 0.8000 0.6000 0.4000 0.2000 0

Execute Statements for Specified Values

for v = [1 5 8 17] disp(v) end

Repeat Statements for Each Matrix Column

for I = eye(4,3) disp('Current unit vector:') disp(I) end

Tips

  • To programmatically exit the loop, use a statement. To skip the rest of the instructions in the loop and begin the next iteration, use a statement.

  • Avoid assigning a value to the variable within the loop statements. The statement overrides any changes made to within the loop.

  • To iterate over the values of a single column vector, first transpose it to create a row vector.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

  • Suppose that the loop end value is equal to or close to the maximum or minimum value for the loop index data type. In the generated code, the last increment or decrement of the loop index might cause the index variable to overflow. The index overflow might result in an infinite loop. See Loop Index Overflow (MATLAB Coder).

HDL Code Generation
Generate Verilog and VHDL code for FPGA and ASIC designs using HDL Coder™.

  • Do not use loops without static bounds.

  • Do not use the and operators within conditions of a statement. Instead, use the and operators.

  • HDL Coder™ does not support nonscalar expressions in the conditions of statements. Instead, use the or functions to collapse logical vectors into scalars.

Introduced before R2006a

You have a modified version of this example. Do you want to open this example with your edits?

You clicked a link that corresponds to this MATLAB command:

Run the command by entering it in the MATLAB Command Window. Web browsers do not support MATLAB commands.

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Select web site

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FOR loops in MATLAB - Basic Tips (Increase Speed etc)

For Loop in Matlab

For Loop in Matlab

Introduction to For Loop in Matlab

MATLAB provides its user with a basket of functions, in this article we will understand a powerful element called ‘For loop’. For loop is a conditional iterative statement used in programming languages. It is used to check for desired conditions and then executes a block of code repeatedly. The block of code is implemented as long as those defined conditions are met. An explicit loop counter is used to distinguish ‘for loop’ from other looping statements. This is also referred to as the loop variable, this allows the loop body to know the sequencing of every iteration. In this topic, we are going to learn about For Loop in Matlab.

Syntax of For Loop:

Now let us understand ‘for loop’ in detail.

Examples of For Loop in Matlab

For index = It will include values, single or multiple statements, and end

This function will run a defined set of statements in the loop for the number of times specified in the condition

Values can have a number of forms e.g:

  • firstVal: lastVal: it will gradually increase the index by 1 from firstval till lastval, it will run the set of statements till firstVal is greater than the lastVal
  • firstVal: step : lastVal: it will gradually increase the index by defined “step” value or it will decrease the value by “step” for negative values
  • valArray: For each iteration, it will generate a column vector from columns of the array for valArray

Now let us use ‘for loop’ in some examples:

Decrement Values

It will decrement the values by the defined interval.

Code:

Here, our output will be decremented by ‘0.5’

Output:

For Loop in Matlab output 1

Let’s take a different decrement interval

Code:

Here is the output that we will get, as we can notice, the values are decremented by 1:

Output:

For Loop in Matlab output 2

Increment Values

It will increment the values by the defined interval.

Code:

Here is the output that we will get, as we can notice, the values are incremented by 1:

For Loop in Matlab output 3

Let’s take a different decrement interval:

Code:

Here is the output that we will get, as we can see, the values are incremented by 2:

Output:

For Loop in Matlab output 4

Specified Values

It will execute statements for specified values

Code:

This is how our output will look like:

Output:

output 5

As we can notice, the values are simply printed.

Use of Repeat Statement for every Matrix Column

Here the eye is a 2X3 Identity matrix

Code:

This is how our output will look like:

Output:

output 6

Use of BREAK Statement

To exit the ‘for loop’ we can use the break statement. Without break, the following example will print the ‘END’ value after every iteration

Code:

This is how our output will look like:

Output:

output 7

If we use it with a break statement, it will break the ‘for loop’ after the first iteration.

Code:

Output:

output 8

As we can notice, our loop is ended after the first iteration.

Conclusion

  • To exit the loop using code, we can make use of break
  • If we want to skip forward coming instructions in ‘for loop’ & begin next iteration, we can make use of continue
  • If we want to iterate over single column vector values, we can first take its transpose to create a row vector.

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Sours: https://www.educba.com/for-loop-in-matlab/

Matlab for loop in

MATLAB - The for Loop



A for loop is a repetition control structure that allows you to efficiently write a loop that needs to execute a specific number of times.

Syntax

The syntax of a for loop in MATLAB is −

for index = values <program statements> ... end

values has one of the following forms −

Sr.No.Format & Description
1

initval:endval

increments the index variable from initval to endval by 1, and repeats execution of program statements until index is greater than endval.

2

initval:step:endval

increments index by the value step on each iteration, or decrements when step is negative.

3

valArray

creates a column vector index from subsequent columns of array valArray on each iteration. For example, on the first iteration, index = valArray(:,1). The loop executes for a maximum of n times, where n is the number of columns of valArray, given by numel(valArray, 1, :). The input valArray can be of any MATLAB data type, including a string, cell array, or struct.

Example 1

Create a script file and type the following code −

Live Demo

for a = 10:20 fprintf('value of a: %d\n', a); end

When you run the file, it displays the following result −

value of a: 10 value of a: 11 value of a: 12 value of a: 13 value of a: 14 value of a: 15 value of a: 16 value of a: 17 value of a: 18 value of a: 19 value of a: 20

Example 2

Create a script file and type the following code −

Live Demo

for a = 1.0: -0.1: 0.0 disp(a) end

When you run the file, it displays the following result −

1 0.90000 0.80000 0.70000 0.60000 0.50000 0.40000 0.30000 0.20000 0.10000 0

Example 3

Create a script file and type the following code −

Live Demo

for a = [24,18,17,23,28] disp(a) end

When you run the file, it displays the following result −

24 18 17 23 28

matlab_loops.htm

Sours: https://www.tutorialspoint.com/matlab/matlab_for_loop.htm
MATLAB For Loop Tutorial

Writing the same thing, again and again, might frustrate you. This is also applicable in programming. There are several situations when a programmer needs to execute a coding program several times.

These program statements are sequentially executed, which means it will first run the first statement, then the second, and so on. Programming languages offer several control structures that grant the execution of complicated programs. This is the same in the case of “MATLAB For Loop”.

Well, Matrix Laboratory or MATLAB is a well-known programming language and multi-paradigm computer environment. It is developed by Mathworks. MATLAB connects computation, visualization, and programming in a simple, usable environment. It is all stated in mathematical equations.

Thus, in this blog, we will study MATLAB “for” loop and “while” loop. But before discussing them, we will explore some uses of MATLAB.

Uses of MATLAB

Matlab is a mathematical computing environment. According to the Matlab website, the environment is created for subsequent uses. 

Now, let’s start discussing the loops in MATLAB.

With the help of a loop statement, the programmer can execute the statements or a group of statements several times. The loops in MATLAB can be understood through the given flow diagram:

Loop Architecture

How do loops in Matlab help you?

Loops help you write the same code repeatedly and minimize your workload to execute similar code again and again.

Suppose a person told you to count to 500, and you have to add 2 to the previous number. You have to start from 1, then move to the next number, +2, the next number, +2, so on. This might be troublesome for you as counting to 500 with adding 2 can be an uphill task for you.

In this case, it is better to use loops in Matlab. The loops are used to perform or iterate a task number of times. This is the power of loops. This is the reason why programmers of most country sites use loops in Matlab to ease their work.

What are the types of loops in Matlab?

Matlab offers the following kinds of loops that handle the requirement of looping a statement. Let’s check all these loops in Matlab:

Loops in MATLAB

While loops in Matlab

It is used to repeat the number of statements or a statement when the given condition is true. It always checks the condition of the loop body before executing it.

Syntax:while <expression>  <statements>end

When an expression is taken as true, then the result of it is nonempty, and it has the nonzero element that might be real or logical numeric. Otherwise, the expression is considered to be false.

Example:Input:b = 1;while ( b < 10 )fprintf(‘value of b: %d\n’, b);b = b+1;EndOutput:Value of b: 1Value of b: 2Value of b: 3Value of b: 4Value of b: 5Value of b: 6Value of b: 7Value of b: 8Value of b: 9

For loops in Matlab

It is used to execute the sequential statement a number of specific times, and it abbreviates the program, which is used to manage the loop variable.

Syntax:for index = values   <program statements>            …end

Here, the values can be of any one kind among these three values that are listed below:

initval:endval:

This value function can be used to increase the index variable that is incremented by 1 from initval to endval, and this will repeat the execution of the code statements until the index has greater value than endval.

Example:Input:for b = 1:10    fprintf(‘value of b: %d\n’, b);endOutput:value of b: 1value of b: 2value of b: 3value of b: 4value of b: 5value of b: 6value of b: 7value of b: 8value of b: 9value of b: 10

initval:step:endval

This is used to increment the index function by the step value for each iteration, and it will decrement the value if the step is negative.

Example:Input:for b = 2.0: -0.1: 1.0   disp(b)endOutput:21.900001.800001.700001.600001.500001.400001.300001.200001.100001

valArray

It is used to create an index of subsequent columns vector from a particular array, for instance: on the initial iteration, index = valArray (:, 1). The loop will execute for the n times, where n is considered to be the number of columns for valArray, which is given by numel(valArray, 1, :). The batch of input valArray involves a cell, string, struct, or cell array.

Example:Input:for b = [12,10,15,22,27]   disp(b)endOutput:1210152227

Nested loops in Matlab

It is used to implement a single loop or more than one loop within other loops in Matlab. This can be done for ”while” loop or “for” loop statements.

Syntax:“For” loopfor m = 1:j   for n = 1:k      <statements>;   endEnd“While” loopwhile <expression1>   while <expression2>      <statements>   endEnd
Example:Input:for a = 2:30   for b = 2:30      if(~mod(a.b))          break; % if factor found, not prime      end    end   if(b > (a/b))      fprintf(‘%d is prime\n’, a);   endEndOutput:2 is prime3 is prime5 is prime7 is prime11 is prime13 is prime17 is prime19 is prime23 is prime29 is prime

MATLAB 2-D Plots Example:

Input:

Output:

MATLAB 3-D Example:

Input:

Output:

Which is better to use for loop or while loop in Matlab?

There is a certain case in which the For loop is much nicer and more compatible. When the user knows the number of iterations that will be done before the loop is started. 

At the same time, the While loop is much nicer in the case when the iterations need to be determined within the loop.

Let’s compare two different codes in terms of while loop and for loop:

for k = 1:20 disp(k);endk = 1;while k <= 20 disp(k); k = k + 1;end

There might be some overlaps, such as executing the iterations until the specific numbers of loops or certain criterion do not reach. In such a case, the loop is most preferred as it reflects the common character of the particular loop.

So, it is easy to say that the user can use the “While” loop when he/she does not have any idea regarding the number of iterations. On the other hand, “For” loops are used when the iteration numbers are known.

List of conditions in which you can use While and For loop!

  • Prefer to use a For loop while you know that the loop must execute n times.
  • Use a For loop for iterating on the columns of array.
  • Practice a while loop if requesting the user’s batch of input.
  • Use a while loop to read a given file within a variable.
  • Practice a while loop method while the increased value is nonstandard.

What is the common difference between While and For loops in Matlab?

ParametersWhile LoopFor Loop
Declaration while ( condition) {statements; //loop body }for(initialization; condition; iteration){//For loop body}
FormatAt the top of the loop, there is only the facility of initialization and condition checking.Condition checking, initialization, iteration statement all can be written at the loop’s top.
ConditionIf there is no particular condition in the while loop, it gives a compiling error.If there is no condition put up within the ‘for’ loop, the loop can easily iterate infinite times.
UseThe ‘while’ loop is practiced only if the number of iterations is not specifically known.The ‘for’ loop is practiced when we already know the number of iterations.
InitializationIn the while loop, if the initialization is performed during condition checking, then initialization is completed every time the loop iterates.Within the ‘for’ loop, once the initialization is done, it will never be repeated.
IterationstatementIn the ‘while’ loop, the user can write the iteration statement anywhere within the loop.In the ‘for’ loop, the iteration statement will be written at the top. Therefore, it will be executed once all statements in the loop are executed.

Loop control statements in Matlab

It is used to change the execution of the normal sequences. Whenever an execution leaves a loop, the elements of the objects will destroy the scope of that particular object. There are two different types of control statements in Matlab:

Break statement

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It is used to terminate the execution of a while or for loops in Matlab. The statements that are defined after the break statement will not get executed. Whereas, in the nested loops, it exists from a specific infinite loop in which it has occurred. The control of the statement is passed to the end of the given loop.

Flow diagram

MATLAB break statement
Example:Input:b = 1;while (b < 10 )   fprintf(‘value of b: %d\n’, b);   b = b + 1;      if( b > 5)         break;      end endOutput:value of b: 1value of b: 2value of b: 3value of b: 4value of b: 5

Continue statement

This statement can pass the control to the upcoming or next iteration in a while or for loops in Matlab. Somehow, it also works as a break statement. Rather than forcing the termination from the loop, it moves to the next iteration of the given loop, and it skips any of the codes in between the program.

Flow diagram:

MATLAB continue statement
Example:Input:b = 1;while b < 11   b = b + 1;    if b == 5      continue;   end fprintf(‘value of b: %d\n’, b);endOutput:value of b 1value of b: 2value of b: 3value of b: 4value of b: 6value of b: 7value of b: 8value of b: 9value of b: 10

Conclusion

Matlab grants the user to use the various kinds of loops in Matlab programming that are used to handle different looping requirements that involve: while loops, for loops, and nested loops. 

Besides these, it also has two different control statements that are: break statement and continue statement, which is used to control the looping of the statement in a program. Using the loops for specific repetitions statements can be a great way to shorten the final coded program. If you have any difficulties related to assignments of Matlab, then you can avail of services for Matlab homework help and Matlab assignment help UK. We have experts team that can be accessible 24/7 with high-quality data. The services are offered at minimal prices, and we can provide you instant help that will deliver the assignments before the deadlines. So, avail of our services, and get relaxed from the complicated Matlab assignments.

Frequently Asked Questions

What are loops in Matlab?

A loop statement enables the user to execute a group of statements or a statement several times. Matlab offers different types of loops to manage looping necessities, including for loops, while loops, and nested loops.

What is a for loop Matlab?

A For loop is used for repetition control structure, enabling the user to write a loop efficiently that requires to perform a specific number of times. The syntax for the ‘for’ loop in MATLAB is as: for index = values.

What is a while loop in Matlab?

The while loop executes the program statement(s) repeatedly as long as the condition remains true. A condition is true till the output is nonempty and includes all nonzero components (real numeric or logical). Otherwise, the condition is false.

Sours: https://statanalytica.com/blog/loops-in-matlab/

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