# MATLAB Octave integral computation help

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1. Apr 20, 2017

### Jacob Marcum

Hello,

I'm having some trouble with my octave coding and would appreciate any input on where the issue lies.
The coding is as follows:

Code (Matlab M):

age = [0:1:100];                            %this is the age matrix, represented by a
time = [0:1:100];                           %this is the time matrix, represented by t

population = zeros(101,101);

for a = 1:101;
population(a,1) = 0.5;                    %this is the initial population
B(a) = (1./(2.*a));                          %this is the birthing probability at age (a)
endfor

for t = 1:100
for a = 2:101
population(1,t+1) = cumtrapz(B(a));     %this is the birth rate
population(a,t+1) = population(a-1,t);    %this is the interation process
endfor
endfor

surf(age,time,population)

The issue I'm having lies in the population matrix computation; the cumtrapz integration is not recognizing the step process and all outputs from t = 2:101 in the population matrix are zeros. I would again appreciate any help to understand where the issue lies.

Thank You,
Jacob M.

Last edited by a moderator: Apr 21, 2017
2. Apr 21, 2017

### Staff: Mentor

You are passing a single element to cumtrapz, not an array.

Explaining what you are trying to do (with equations) would help.