How to write this loop?

%% readDataFromFile and WriteDataToFile are given functions
%% stress.out is a file containing a matrix of 195 elements

function calculateStressVonMises('stress.out')
 
    readDataFromFile('stress.out');
    sigmaV_matrix = [];
    
       for c = 1: 1: 194
        i = 2
        j = 3
        k = 4
  
        sigmaV(c) = sqrt((c(i))^2 - (c(i))*(c(j)) + (c(j))^2 + 3*(c(k))^2);
        
        sigmaV_matrix = [sigmaV_matrix; {sigmaV}];
        
        writeDataToFile('stress.out', sigmaV_matrix)
       end 

[Walter Roberson]

Your question is not clear. Are you trying to index only the first 194 elements? Are you trying to index in groups of 194 elements and then the next group of 194 until the end of file? Your c would be a vector if it were not empty; c = c + 1 would increase all of the values in the vector by 1; is that what you want to do? If so then it would be more efficient to record c(i), c(j), c(k) and increment them by 1 instead of keeping the whole vector around and incrementing it.

[Walter Roberson]

function calculateStressVonMises('stress.out')
 
    readDataFromFile('stress.out');

should be replaced with

    function calculateStressVonMises(filename)
    if ~exist(filename, 'var'); filename = 'stress.out'; end
    readDataFromFile(filename);

[Walter Roberson]

is readDataFromFile('stress.out') a function that returns a value? Is it a function that uses assignin('caller') to write a variable into the workspace of the function that calls it?

[Adam Danz]

Similar query by OP (just noticed this thread)

https://www.mathworks.com/matlabcentral/answers/497141-index-in-a-matrix-into-an-equation

[Rena Berman]

(Answers Dev) Restored edit

Answer 1

[Walter Roberson]

%% readDataFromFile and WriteDataToFile are given functions
%% stress.out is a file containing a matrix of 195 elements
    function calculateStressVonMises(filename)
        if ~exist(filename, 'var'); filename = 'stress.out'; end
        data = readDataFromFile(filename);
        
        sigmaV = sqrt(data(:,2).^2 - data(:,2).*data(:,3) + data(:,2).^2 + 3*data(:,4).^2);
            
        writeDataToFile('stress.out', sigmaV)
    end 

There is a possibility that the last line should instead be

    writeDataToFile('stress.out', num2cell(sigmaV,2) )

[Walter Roberson]

That would be correct for running the code.