"Index exceeds matrix dimensions"

When I use the function r() in a for loop I get the error "Index exceeds matrix dimensions."

is a function defined in it's own .m file as:

 function [dist] = r(a,e,theta)
%function [dist] = r(a,e,theta)
%Computes the distance from the center of the planet to the spacecraft
dist = a.*(1-e.^2)./(1+e.*cos(theta));
end

Main file starts here

 a=5;
theta = [0:pi/100:2*pi];
e = [.1 .3 .5 .7 .9];
figure (2)
plot(Xearth,Yearth,'g')
hold on
axis equal
for i = e
    %r = a.*(1-i.^2)./(1+i.*cos(theta)); %works properly with this instead but want to use fucntion
    r = r(a,i,theta);    %error points to this line
    x = r.*cos(theta);
    y = r.*sin(theta);
    plot(x,y)
end

Answer 1

[Walter Roberson]

Your line

      r = r(a,i,theta);    %error points to this line

says that the knowledge that r is a function is to be overridden to make r a numeric variable, the result of calling the function the first time. Then in the second time through the loop you try to access the numeric variable as if it it were a function.

Do not name your variables the same thing as any function that you might use. (Also do not name your variables the same thing as any of the common MATLAB functions such as "sum" or "image", as you will make this kind of mistake when you do, and you will confuse other people who have to read your code.)