Calculate convolution using DFT, FT and IFFT

I'm converting the cosine transform into an integral in convolution form, because :(1) using logarithmic coordinate sampling is suitable for my subsequent work; (2) There is an analytic expression for the Fourier transform of the cosine term after converting.

However, my calculation results are not consistent with those of MATLAB command conv. Please give me some advice.

Thank you!

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