Values used to run a for loop

Hi, I'm trying to model the strength of a cable that consist of N wires, subjected to strain loading (epsilon). To find the strength of the cable I use 2 for loops and some IF sentences. Since I want to find the strength of the cable based on the strain, I want epsilon to start at zero and calculated at certain steps (a in script) towards a described end value (k in script). If I start with epsilon = 0 then I get: Attempted to access jobb(0); index must be a positive integer or logical. Is there a way that my epsilon value can go from zero and I can have smaler calculation steps than 1? The script works when epsilon = 1 and step = 1..

Here is my script:

clc; clear all; close all;  
  E = 7.75*1e4;
  Area = 38.48;
  my = 0.8686;
  sy = 0.1318;
  mu = 0.4343;
  su = 0.3295;
  k = 8;                                                                      
  a = 1;
  N = 200;                                                                    
  epsilon_0 = 0;                                                                                                                                    
  jobb = zeros(k,1);                                                          

    P = rand(N,1);                                                          
    epsilon_y = logninv(P,my,sy);                                           
    epsilon_u_y = logninv(P,mu,su);                                         
    epsilon_u = (epsilon_y + epsilon_u_y);                                  
    n = numel(P);                                                                                                                               
    g = 1:a:k;                                                                                                                       
    model = zeros(n,1);                                                     

    for epsilon = (0+epsilon_0):a:k;                                            

        for ii = 1:n;                                                           
        if epsilon_y(ii) >= epsilon                                             
            ep = epsilon;                                                       
        elseif epsilon_y(ii) < epsilon && epsilon < epsilon_u(ii)
            ep = epsilon_y(ii);
        elseif epsilon_u(ii) <= epsilon
            ep = 0;
        end
        model(ii) = ((ep/100)*E);                                               

        end
        p = sum(model)*Area;                                                    

        jobb(epsilon) = p;                                           

    end

Best regards

Trond Oesten

Answer 1

[Michael Haderlein]

First, you need to distinguish between an index and a value. When you want to assign a value to jobb(epsilon), epsilon is an index. In Matlab, index are integers >=1. Thus, zero is not allowed. In your case, you better create some counter for your outer loop such as you did for the inner loop and work with epsilon(jj) (jj being the counter here). Then, jobb(jj) corresponds to epsilon(jj) and everything is clear.

Apart from that, I think your script can be vectorized. You might want to think about it. If you need help with this respect, please write here again.