Problem with equation input

>>r= APR/1200
A= 200000
APR= [4,5,6]
M= [36,48,60,72]

These are my variables When I put my formula in matlab i get this message

>> P= (A*r*(1+r)^M)/(((1+r)^M)-1)
Error using  ^ 
Inputs must be a scalar and a square matrix.
To compute elementwise POWER, use POWER (.^) instead.

So i replace the ^ with .^ and i get this message instead:

>> P= (A*r*(1+r).^M)/(((1+r).^M)-1)
Error using  .^ 
Matrix dimensions must agree.

Does anyone know what is wrong with my equation and what I can do to fix it?

Answer 1

[Star Strider]

There are more efficient ways to approach this, but probably the easiest is to use a for loop:

A= 200000;
APR= [4,5,6];
M= [36,48,60,72];
for k1 = 1:length(APR)
    r = APR(k1)/1200;
    P(k1,:)= (A.*r.*(1+r).^M)./(((1+r).^M)-1);
end

I am not certain what you want to do, but this is one solution. It uses ‘APR’ to define the array size, and computes ‘P’ for all values of ‘M’ for each value of ‘APR’.

Note that I completely vectorised your ‘P’ assignment. See the documentation for Special Characters, ‘Array Indexing’, Array vs. Matrix Operations, and for loops.

[Amaya]

Thank you for taking the time to answer the problem! When I input your version is still got:

 "Error using  .^ Matrix dimensions must agree."

I'm trying to get the equation right so I can get values and use it for later parts which ask me to make a chart.

[Star Strider]

My pleasure.

It ran without error for me, or I’d not have posted it. Did you copy my code from my Answer and paste it into the MATLAB Editor and run it?

What code did you run? Please post all of it.

[Amaya]

Thank you! It worked, I didn't copy the for and end and now it works, thank you!

[Star Strider]

My pleasure!

There are version differences (I’m using R2014b), so I was ready to troubleshoot those if you had problems running my code in an earlier version. I’m glad that was not necessary.