Array indices must be positive integers or logical values error

%HW4 Q2-Vector Loop solution
r2=1; r3=4;
theta2=60;
X = (2*r2((cosd(0)*cosd(theta2))));
B=r2^2-r3^2;

%Case 1 - signma=+1
sigma=1;
r1=(-(-X)+sigma*sqrt(X^2-4*B))/2;
theta3=atand((-r2*sind(theta2))/r1*cosd(0)-r2*cosd(theta2));

%Case 2 - sigma=-1
sigma=-1;
r1=(-(-X)+sigma*sqrt(X^2-4*B))/2;
theta3(2)=atand((-r2*sind(theta2))/r1*cosd(0)-r2*cosd(theta2));

The error is on line 4 for 'X' variable

[the cyclist]

FYI, I edited your question to use the "code" format from the toolbar, to make it more readable. Next time, please take a look at doing that yourself.

[Haren Sunil Panchal]

Ok, Sorry for that

Answer 1

[the cyclist]

You need

X = (2*r2*((cosd(0)*cosd(theta2))));

instead of

X = (2*r2((cosd(0)*cosd(theta2))));

(Note that I used r2* instead of just r2.)

MATLAB needs the explicit multiplication sign there, to distinguish the syntax from indexing a variable (which is why it threw that error).

[Haren Sunil Panchal]

Thank you. This helped me resolve the issue.