Don't understand indexing statement from compiler

MY code is:

function mbd = spherical_mirror_aberr(fn,D )
%SPHERICAL_MIRROR_ABERR Summary of this function goes here
%   Detailed explanation goes here
delta_x = 0.01;
Num_x=D/2/delta_x;
f = fn * D;
delta_theta = asin(delta_x/(2*f));
D_theta = asin(D/2/(2*f));
theta(0: delta_theta:D_theta);
Mult = 8*delta_x/D^2;
mbd =Mult*sum( 2*f*tan(2*(0:delta_theta:Dtheta))(1/cos(0:delta_theta:D_theta) -1)); 
end

The compiler is giving me a warning: "indexing must appear last in an index expression" What does this mean that I need to do. It affects the "mbd" variable equation.

[Guillaume]

Please don't add comments as answers

DJ V comment posted as an answer moved here:

function mbd = spherical_mirror_aberr(fn,D )
%SPHERICAL_MIRROR_ABERR Summary of this function goes here
%   Detailed explanation goes here
delta_x = 0.01;
Num_x=D/2/delta_x;
f = fn * D;
delta_theta = asin(delta_x/(2*f));
D_theta = asin(D/2/(2*f));
theta(0: delta_theta:D_theta);
Mult = 8*delta_x/D^2;
mbd =Mult*sum( (0:delatax:D/2)*2*f*tan(2*(0:delta_theta:Dtheta))(1/cos(0:delta_theta:D_theta) -1)); 
end

THe error still exists, but the above code at least includes X.

[Guillaume]

As per comments to Adam's answer, you're still missing a *.

[DJ V]

     I simplified the code considerably just to begin to find the error:

Now it produces:

Error in spherical_mirror_aberr (line 10)

mbd =Mult*sum( (0:delatax:D/2));

[Adam]

Errors come with an error message, not just a line number usually.

Answer 1

[Adam]

sum( ... )( ... )

is not valid syntax in Matlab.

You can't chain together parenthesis is what that error is essentially sayiing. I don't really know what you are trying to do in the expression. Maybe you are just missing a * from between the ) and the (

[Guillaume]

It's actually

tan( 2*(...) )( ... )

that is causing the problem. It does look like you're missing an operator.

I would recommend using more white spaces in your expression and if necessary continuing on the next line (with the ... operator). At the very least be consistent. The

longexpression -1

in particular, I find very bad style. Either use

longexpression - 1

or

longexpression-1

Also, the line

theta(0: delta_theta:D_theta);

does not do anything since the result of the indexing is not assigned anywhere or displayed.

[DJ V]

But I have parentheses around the entire equation. It should see that. Your response doesn't make sense. The equation I'm trying to enter is: 2*f*tan(2*theta)*(1/cos(theta) -1)

[Guillaume]

Well, you're missing the * between 2*f*tan(2*theta) and (1/cos(theta)-1)

[Image Analyst]

Since your theta is actually an array of theta's, you'll need dot slash instead of slash: 1./cos(). You'll also need a dot * instead of * almost everywhere, for example tan() .* (1./cos)

Answer 2

[DJ V]

BUt in the code as written now there is no multiplication or division,and it still won't work.