Error: Attempt to reference field of non-structure array.

Hi, I'm trying to figure out why I'm getting this error in my code. Here's my code, and underneath is an explanation of what it does. v=.25:.25:40; T, Rev, J, Cp, Ct, n, H, Vbar, vs and Rw are all functions of v, so they're arrays too. Here's where it gets complicated.

syms y;
Aa=(32.*(Cp./(2*pi)).*(1-Ct).^.5./(pi.*J.^2.*(1.+(1.-Ct./(1.-Ct))))).*y./Rw;
c=1.2954.*heaviside(.038815-y)+(((1.524./2).^2-(y+.5).^2).^.5).*heaviside(y-.038815);

So there's that, which represents a variable Aa depending on y, valid from -Rw<y<Rw at whatever v is being used at the moment. C however, goes from quite a bit less than -Rw to just a bit above Rw.

Then I try to calculate my lift coefficients. Cls is for -Rw to Rw and Cl includes the part of the wing outside that. There's two for loops iterating through v and alpha outside of these.

 Cls=vpa((6.02293*sin(alpha(i))/2*(1+4/pi*(1.688466196366/c)*(1-((.5+y)/(1.52401))^2)^.5)*(1/2*1.185*v(j)^2)/(1/2*1.185*vs(j)^2)+1.87*(Rw(j)/c)*(1-(v(j)/vs(j))^2)*(0-Aa(j))/(pi^2/4-1)*(1/(y/Rw(j))-(y/Rw(j)))*log((1+y/Rw(j))/(1-y/Rw(j)))));
        Cl=6.02293*alpha(i)*heaviside(-(Rw(j)+y))+Cls*(heaviside(Rw(j)-y)*heaviside(Rw(j)+y))+6.02293*alpha(i)*heaviside(y-Rw(j));

My problem comes after this. I need to integrate 1/2*1.185*v^2*c*Cl from -.5 to .262, which is the span of the wing.

L(i,j)=2*int(1/2*1.185*v(j)^2*c*Cl,y,-.5,0.262005);

This line is what gives me the error. I don't know why, and I'm getting annoyed at this program. So if anyone has any advice on how to fix it, or perhaps simplify my code so I never need to do whatever causes the error, I would be grateful.

Thank you.

EDIT: Good News/Bad News. The error is gone, replaced by a different error that I do know what means. Unfortunately, it takes near 3 hours to perform one of a couple thousand calculations. So. I could use help optimizing the code to run faster, if anyone would like to volunteer.

[Jan]

Please post an exact copy of the error message.

[Walter Roberson]

Someone had a very similar problem a week ago; see http://www.mathworks.com/matlabcentral/answers/15793-attempt-to-reference-field-of-non-structure-array

[JH]

Thank you Walter. I did see that question when googling the error, but I already checked to make sure that wasn't it. As you can see now in my edit, MATLAB gave a different error this time, which I can fix.

Apparently, it wanted vpa(int(...)) to convert the result into a double. I don't know why this initially resulted in the original error, but I'm just glad it threw an error I could fix.

Answer 1

[Jan]

I'm getting nervous when I see constructs like ".^.5./". They make me start to think, and thinking is prone to errors. I strongly suggest to use 0.5 instead of .5 and insert spaces around the operators to avoid ambiguities.

Are you sure, that there is no lowercase L instead of a 1 (one)?

Does the error appear in the posted line, or inside the INT command?

[JH]

I'm sorry I haven't posted the whole error yet. This is a terribly slow piece of code, but I don't know enough about what MATLAB can and can't to do to speed it up.

Everything functions until the line with the integration. I can plot Cls and Cl along y at different values of v and alpha no problem. When the error comes up, it only mentions the L(i,j)=...

As soon as it finishes running, I'll post the error again. The terrifyingly long running time would have been a tip off something was wrong, but I didn't notice last time, as I was at lunch.

I think it might be simply broken now. It's been running for almost 2 hours. And it is indeed stuck on the L(i,j)= line, and it has finished calculating everything before that point.

Answer 2

[Image Analyst]

Since this line

L(i,j)=2*int(1/2*1.185*v(j)^2*c*Cl,y,-.5,0.262005);

is what throws the exception, and structure members are to the right of dots, I'd say that it thinks either 185 or 262005 is a member of a structure, so it must think 1 or 0 is a variable. Like Jan said, are you sure it's a one and not the lower case letter L and a zero and not the letter O?

Finally, I don't know what int() is. Are you sure it takes 3 arguments? Did you mean int32()? For int() it says this, which I don't understand:

int

 int   Convert a FILTSTATES.CIC object to an integer matrix.
    int(Hs) returns an signed integer matrix for the FILTSTATES.CIC
    object.

    EXAMPLE:
    Hm = mfilt.cicdecim;
    hs = Hm.states; % Returns a FILTSTATES.CIC object
    states = int(hs); % Convert object to a signed integer matrix.

See also
FILTSTATES/CIC.

I have no idea what a "FILTSTATES.CIC object" is.

[JH]

That line is a direct copy from my code, and you can see that those are numbers, not letters. The int() function is symbolic integration.

http://www.mathworks.com/help/toolbox/symbolic/int-integral.html