How do I create a for loop in MATLAB?

I am completely lost in for loops, I just don't get it. The book and my professor haven't helped much. Where can I get help?

[Abderrahmane Walid AISSANI]

hi I am trying to create several variables using the for loop

    % for k=1:1:10
      tab_k = csvread('');
      end

in fact the code is wrong but I want to iterate the "k" in the name of the variable but I can't find how to do that .

thank you .

[Walter Roberson]

http://matlab.wikia.com/wiki/FAQ#How_can_I_create_variables_A1.2C_A2.2C....2CA10_in_a_loop.3F

http://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

Answer 1

[Walter Roberson]

A basic for loop in MATLAB is often used to assign to or access array elements iteratively. For example, let’s say you have a vector A, and you want to simply display each value one at a time:

A = [3 6 9 4 1];

for i = 1:length(A)
       disp(A(i))
end

For more examples using for loops, see:

https://www.mathworks.com/help/matlab/ref/for.html

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

[Patrik Ek]

As far as I know the for-loop is even more excellent than what says in this text. As far as I know the matlab for-loop works similar to the for_each-loop that can be seen in many programming languages these days, or maybe the range-for in c++11. For example is this possible,

a = aObjArray;
for k = a
  a.modify();
end

This is not really clear from the documentation, so I thought this would be a valuable comment.

[帅 赵]

but it doesn't work

[Walter Roberson]

Not sure why it is said that it doesn't work?

A = [3 6 9 4 1];

for i = 1:length(A)
       disp(A(i))
end

     3

     6

     9

     4

     1

[Jake Dalrymple]

This is very helpful! How could you display these values in rows of 5 rather than just one value per row?

[Walter Roberson]

@Jake Dalrymple

A = randi([0 9], 1, 20)

A = 1×20

1 9 5 8 6 2 6 2 2 0 3 2 1 4 7 3 9 7 2 6

%then output in groups of 5 in vectorized form
reshape(A, 5, []).'

ans = 4×5

1 9 5 8 6 2 6 2 2 0 3 2 1 4 7 3 9 7 2 6

%or if you need a for loop
for K = 1 : 5 : numel(A); disp(A(K:K+4)); end

     1     9     5     8     6

     2     6     2     2     0

     3     2     1     4     7

     3     9     7     2     6

Matters get more complicated if the number of entries in the array is not a multiple of the number of columns you want to use. For example,

A = randi([0 9], 1, 23)

A = 1×23

9 6 1 5 7 4 8 4 8 4 4 5 8 5 3 6 9 2 1 4 8 9 9

for K = 1 : 5 : numel(A); disp(A(K : min(end,K+4))); end

     9     6     1     5     7

     4     8     4     8     4

     4     5     8     5     3

     6     9     2     1     4

     8     9     9

Answer 2

[Jan]

You can get help from the documentation of Matlab:

doc for
help for

There you find examples and explanations.

[Meenakshi Bhardwaj]

Thanks so much. Finally, I understood what is for loop.

Answer 3

[Jan Afridi]

For loop repeat itself for a given number of input. The syntax for “For Loop Matlab” is

for variable = expression
Program Statement
end

In the above syntax, the expression has one of the following forms.

Initial value : Final value

for x = 1:10 
fprintf('value of x: %d\n', x); 
end

Initial value : Step : Final value

for x = 1:2:10
fprintf('value of x: %d\n', x); 
end

Value Array

for x = [1 4 6 8 90]
disp(x) 
end

To learn more about in detail visit this link For Loop Matlab

Answer 4

[mohamed mohamed]

for x = 1:10 
fprintf('value of x: %d\n', x); 
end

value of x: 1
value of x: 2
value of x: 3
value of x: 4
value of x: 5
value of x: 6
value of x: 7
value of x: 8
value of x: 9
value of x: 10

Answer 5

[Narasimman P]

for a=1:10
end

[Ealam Yassin]

no output

[Walter Roberson]

@Ealam Yassin

The code posted by @Narasimman P is a completely valid for loop, just one that does not do anything inside the loop. All it does is count from 1 to 10 internally. After the loop, two things will have changed:

1. Time will have elapsed, which could be important if you are waiting for something to happen
2. The loop control variable 'a' will have the same value as it was last assigned, so in this case after the loop 'a' will have the double precision value 10 .

disp('before')

before

whos

disp('starting loop')

starting loop

for a=1:10
end
disp('after')

after

whos

  Name      Size            Bytes  Class     Attributes

  a         1x1                 8  double              

So there has been output: the variable a did not exist before, and after the loop it does exist.

Answer 6

[Manan Shah]

for i = 0:8 ;
    a = pow10 (i);
    disp a(i);
end

[Walter Roberson]

 disp a(i)

would mean the same thing as

disp('a(i)')

You probably want

disp(a(i))

Answer 7

[Iosif]

D=input ('Βαθος νερου σε m ')
W=input ('Βαρος ανα μοναδα μηκους της γραμμης αγκυρωσης στο νερο σε N/m ')
Hex=input ('εξωτερικη φορτηση σε kn ')
dx=input ('οριζοντια μετατοπιση σε m ')
if dx/D>=0.3 && dx/D<=0.6
else
    disp ('Δωσε διαφορετικη τιμη για το dx')
    dx=input ('οριζοντια μετατοπιση σε m ')    
end

I want to make my programm go to if after else and run that lines again until if line is satisfied

[Walter Roberson]

while ~isnumeric(dx) || ~isscalar(dx) || dx/D<0.3 || dx/D>0.6
    disp ('Δωσε διαφορετικη τιμη για το dx')
    dx=input ('οριζοντια μετατοπιση σε m ')    
end

Answer 8

[Kartick]

There are 4 type of loops: while, for, if and case.

For loop :

Eg: you have your robot whom you wish to give command to walk 100steps. The command will be

for steps=1:100
end
disp(steps)

   100

The robot will go 100steps and stop and output will be displayed as 100 after completion.

For loop is used to solve many mathematical problems like factorials etc.

[Walter Roberson]

Computer Scientists use the term "control statement" for code structures that will execute selectively exactly zero or one time. Computer Scientists use the term "loop" for code structures that have the potential to execute more than one time. "if" and "case" are control structures but are not loops.

If you imagine the execution point as starting from the "top" and falling downward, then "if" and "case" only ever have the execution point continuing to fall downwards, whereas "for" and "while" in general require pumping the execution point back up again.