Rakesh Kumar B.

asked • 11/30/13

Array in matlab

I'm trying to set up a matrix of variable length with two columns into which I can store the results of a for loop. The length will be determined by the number of iterations of the loop.

Rakesh Kumar B.

I mean to say, when one enters the value of variable n,
my program asks the user to enter the matrix elements. After the user is finished with entering the element my program shall display the matrix elements in matrix form.
In my program the number of row increases but the column is fixed to two.
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11/30/13

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Nathan C. answered • 11/30/13

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It is better to set the size of the matrix before the for loop. Typically, with a for loop, you know the number of iterations, even if it is a variable.
 
------------------
% where "n" is determined earlier in the script
 
results_matrix = zeros(n,2);
   
% creates a matrix filled with zeros of dimension n rows and 2 columns
 
for i_number_of_loop = 1:n
results_matrix(i_number_of_loop, :) =...
   [i_number_of_loops, i_number_of_loops*n]
 
% this populates the matrix
% You'd insert your calculations here
 
end
 
--------------------------------------------
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Rakesh Kumar B.

Thanks Nathan, for the answer. But actually I want to enter the matrix elements manually while then program is running.
 
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11/30/13

Nathan C.

Use the "input" function
http://www.mathworks.com/help/matlab/ref/input.html
 
You can use it to ask the user how many rows, then store the variable:
 
n = input('How many rows?');
 
 
Then have them enter each row from inside the for loop:
 
results_matrix(i_number_of_loop, :) = input('Enter the row using the notation [#,#]');
 
 
 
Of course, unless the for loop is necessary for the assignment, you could just have the user enter the entire matrix without a for loop:
 
results_matrix = input('Enter the entire matrix using the notation [#,#;#,#;#,#;...;#,#] where the commas separate the columns and the semicolons separate the rows');
 
 
Lastly, you can do a while loop instead of a for loop, not ask the user for the number of rows in advance, and just have them hit "enter" when they have no more rows to enter...
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11/30/13

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