Problem with variable size

Question

Catteau Ophélie 2021-3-24

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/782433-problem-with-variable-size

评论： Walter Roberson 2021-3-24

Hello, I am trying to do a customize buffer but it says that my output has a variable size and I don't wont it.

Can someone help me to resolve it ? I put my code below ( u is a vector of 8 double and FFTLength is a size of the buffer)

function data = custom_buffer( FFTLength, u)
%#codegen
persistent buffer next_index
% Define initial values
if isempty(buffer)
    buffer = zeros(FFTLength,1);
    next_index = 1;
end
% Populate the buffer
for k = 1 :8
    buffer(next_index) = u(k);
end
% Increment the location to write to at the next time
if next_index < FFTLength
    next_index = next_index + 9;
else
    next_index = 1;
end
    data = buffer;
end

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Catteau Ophélie 2021-3-24

在 MATLAB Online 中打开

OK, thank you I forgot this, I change it but it doesn't solve my problem about the variable size of data.

function data = custom_buffer( FFTLength, u)
%#codegen
persistent buffer next_index
% Define initial values
if isempty(buffer)
    buffer = zeros(FFTLength,1);
    next_index = 1;
end
% Populate the buffer
for k = 1 :8
    buffer(next_index) = u(k);
    next_index = next_index +1;
end
% Increment the location to write to at the next time
if next_index < FFTLength
   next_index = next_index + 1;
else
    next_index = 1;
end
    data = buffer;
end

Walter Roberson 2021-3-24

No, that way of coding can expand the array.

Suppose that we have reached next_index = FFTLength - 1. Then buffer(next_index)=u(1) puts u(1) into second last location, increment next_index to FFTLength - 0. u(2) is put there, increment next_index to FFTLength + 1. u(3) is put there... Ooops, we expanded the array!

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Answer 1

Walter Roberson 2021-3-24

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/782433-problem-with-variable-size#answer_657093

在 MATLAB Online 中打开

function data = custom_buffer( FFTLength, u)
%#codegen
persistent buffer next_index
% Define initial values
if isempty(buffer)
    buffer = zeros(FFTLength,1);
    next_index = 1;
end
% Populate the buffer
for k = 1 : 8
    buffer(next_index) = u(k);
    next_index = mod(next_index, FFTLength) + 1;
end
data = buffer;
end

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Catteau Ophélie 2021-3-24

I corrected like to write but there is always the variable size 's issue...

Walter Roberson 2021-3-24

在 MATLAB Online 中打开

Is your FFTLength input defined as a Constant block? If there is any chance that the value could change between function calls, then the block is variable length.

The typical work-around for this is to define a maximum length using coder.varsize() or to

buffer = zeros(maximum_FFTLength,1);

and

assert(FFTLength <= maximum_FFTLength)

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