Array indices must be positive integers or logical values.

I am not sure why my code is coming up with this:

Array indices must be positive integers or logical values.

Error in P9_07_Casey_Galerneau (line 18)
    monthly =
    principal*((interest(1+interest)^number_payments)/((1+interest)^number_payments)-1); 
>>

[Casey Galerneau]

for interest = 0.0025:0.0025:0.05
    number_payments = years*12;

      monthly = principal*((interest(1+interest)^number_payments)/((1+interest)^number_payments)-1);
      fprintf('     %4.2f             %7.2f', interest, monthly);
  end

[Casey Galerneau]

I have double checked what I could but the only factor that I think is causing issues is that interest is less than 1?

[Casey Galerneau]

The interest is starting at 0.0025 and going up to max of 0.05 in increments of 0.0025, I believe I need to use a while grouping but now my code is giving a different error from the previous one.

Invalid expression. Check for missing or extra characters.

interest = 0.0025;

while interest <= 0.05

for

     fprintf('****************************************************\n');

     fprintf('           MORTGAGE PAYMENT CALCULATIONS\n');

     fprintf('\nPrincipal = $%6.0d\n\n', principal); 

     number_payments = years*12;

     top = (interest(1+interest)^number_payments);

     bottom = ((1+interest)^number_payments)-1;

     monthly = principal*(top/bottom);

     fprintf('Interest Rate     Monthly Payment\n');

     fprintf('     %4.2d             %7.2d', interest, monthly);

end

interest = interest + 0.0025;

end

[Walter Roberson]

You have a for keyword that is not followed by variable = expression

[Casey Galerneau]

It highlights the "for" line of the code as the variable/expression that is missing a keyword or end line of code, it has a corresponding end, so I am at a loss to what is wrong. As far as I know this statement should work otherwise?

[Stephen23]

" As far as I know this statement should work "

When I looked at the for help age it shows just one syntax, which does not match how you are using it. Can you please explain how your syntax (not supported by the MATLAB documentation) "should work".

[Walter Roberson]

"for" must be followed in the same line by something in the form of an assignment.

[Casey Galerneau]

principal = input('Enter principal in dollars: ');

years = input('Enter number of years: ');

interest = 0.0025;

number_payments = years*12;

top = (interest(1+interest)^number_payments);

bottom = ((1+interest)^number_payments)-1;

fprintf('****************************************************\n');

fprintf(' MORTGAGE PAYMENT CALCULATIONS\n');

fprintf('\nPrincipal = $%6.0d\n\n', principal);

while years <= 30

    for interest = 0.0025:0.0025:0.05

       monthly = (principal*(top/bottom));

       fprintf('Interest Rate     Monthly Payment\n');

       fprintf('     %4.2d             %7.2d', interest, monthly);

    end

end

Ok, now I really don't understand. I am getting this error after all of this code:

Array indices must be positive integers or logical values.

Error in P9_07_Casey_Galerneau (line 11) top = -(interest(1+interest)^number_payments);

Answer 1

[Walter Roberson]

interest(1+interest) attempts to index the vector or array interest at location(s) 1+interest . That is not necessarily impossible -- for example if interest = [0 1 2] then 1+interest would be 1 2 3 and interest([1 2 3]) would be valid. It is, however, rather suspect.

You should probably recheck your formula to see whether the formula asked for indexing at that point, or asked for multiplication.

[Casey Galerneau]

How do I make it ask for multiplication?

[Walter Roberson]

Put * between the two terms that are to be multiplied.