Conversion to double from struct is not possible.

To make a visualization of a function inside of a loop i used getframe. If i don't specify a number after the variable it only saves the last frame so i used this code

OBS(counter) = getframe;

Where OBS will be later used in movie(OBS) and the counter is the same counter as used in the loop. In a muck up code, this worked perfectlty. But in my main code it gives the error message: Conversion to double from struct is not possible. I know OBS here is the construct. Counter can't be it is equal to 1 ( i can see that in the workspace). OBS is a global, but that shouldn't be the issue.

the code where it works is

counter = 1;

for k = 1:16 plot(fft(eye(k+16))) axis([-1 1 -1 1]) PAR(counter) = getframe; counter = counter +1; end

pause figure movie(PAR)

i'm stuck on this, thanks for any tips or help Bert

[Rik]

Using a global can lead to really weird bugs. You should use functions to pass variables (or in GUI you can use guidata).

Try to condense your problem to the shortest code that fails, because now there isn't anything to debug.

(next time, use the {}Code button to properly format your code)

[Bert Taekels]

I believe the problem is, that i create the global before i use it ( which is the logical way). This way the global is defined as a double where the getframe function expects a construct and gives the error. I should then either clear the global (which worked on the function level of my code, but gave other issues) or define the global as construct to begin with. I have yet to find out how that has to be done, but i think that will solve my issues

[Stephen23]

"OBS is a global, but that shouldn't be the issue."

Famous last words. Avoid using globals. Pass variables properly.

Answer 1

[Guillaume]

As has been said and will keep being said, using globals is a mistake. While it may work fine for now with your simple code, it will bite you back as the code becomes more complex.

Anyway, your problem is indeed that you cannot assign a structure to something by indexing into it if that something is not a structure with the correct field. You can solve your issue by declaring that something as an array of empty structures with the correct fields:

numelem = 16;  %or whatever number of elements you're predeclaring
OBS = struct('cdata', cell(1, numelem), 'colormap', cell(1, numelem));  %predeclare struct array
%...
for counter = 1:numelem
   OBS(counter) = getframe;  %will not error 
end