Using the previous cumsum value of a for loop to calculate a new value

hi, i have a code in which in a for loop the cumulative sum of the equation needs to be used in the next loop and then put into another equation but i am having issues with matrix/array sizes.

This is my code:

A=9.41e-17;
n=5.5;
m=0.02;
B=1.054e-13;
phi=6.5;
x=4.44;
sigma=80;

%time stetup
timei=0;
timef=100;
dt=0.02;
timestep=(timef/dt)+1;
time=linspace(timei,timef,timestep);
for jj=1:timestep
   if jj==0
     w=0;
   end     
   t=time(jj);
   dw=B*(sigma/((1-w*(jj))^phi))*(t^m)*dt;
   w=cumsum(dw);
   de(jj)=(A*((sigma/((1-w))^n))*t^m*dt);
   e=cumsum(de);
end

For this calculation the cumulative value of w has to be used to find the next change in w, the cumulative sum of w then has to be used to find the change in e and then the sumulative sum of e is then plotted against the time vector.

The issue i am having is when i create the vector dw by adding (jj) after it this error appears:

Incorrect dimensions for raising a matrix to a power. Check that the matrix is square and the power is a scalar. To perform elementwise
matrix powers, use '.^'.
Error in TEST (line 33)
    de(jj)=(A*((sigma/((1-w))^n))*t^m*dt);

if i use'.^' the matrix dimensions do not agree.

Any advice is welcome, thanks

[dpb]

...
for jj=1:timestep
   if jj==0
     ...

jj can never be zero...looks like you just need to initialize w to 0 before the loop begins, probably.

It would seem you don't need cumsum to build a vector but just sum(dw) for each step to use as the w for the next.

If you want to plot e as you go, do it then or save it in a vector for later, but each iteration is just a single value.

[DECLAN O RIORDAN]

thanks for the reply,

sorry that jj should have been 1. i have now an issue of mismatched sized matrices as seen below

[dpb]

You still don't need the if jj block in the loop; just initialize w before the loop begins.

And you reference (1-w) in the offending line, not w(jj) which is the new summation.