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What is the Fourier transform of the identity function?



The 2019 Stack Overflow Developer Survey Results Are InWhat's the Fourier transform of these functions?Fourier transform of the identity function $f(x)=x$Fourier Transform Dirac DeltaDirac delta distribution and fourier transformFourier transform of distribution without physicist's $delta$-functionfourier transform normalization constantComputing Fourier TransformFormal derivation of the Fourier transform of Dirac delta using a distributionFourier transform using Dirac'sFourier Transform of Heaviside Step Function










0












$begingroup$


How to find the Fourier transform of $x mapsto x$ using distribution $delta$?



Since $FT(1)=sqrt2pi delta(k)$ then $FT(x cdot 1)=sqrt2pi i delta'(k)$



But also since $1=d/dx (x)$ then $FT(x)=FT(1)/(ik)=delta(k)/(ik)$



Are both of these correct?










share|cite|improve this question











$endgroup$











  • $begingroup$
    You are not really allowed to write $delta(k)/k$ in distribution theory, but the best interpretation if this expressions is $-delta'(k)$.
    $endgroup$
    – md2perpe
    Mar 30 at 16:22











  • $begingroup$
    Your first derivation is correct.
    $endgroup$
    – md2perpe
    Mar 30 at 16:26










  • $begingroup$
    Your second derivation lacks a term $C , delta(k)$: $$sqrt2pi , delta(k) = FT(1) = FT(fracddxx) = ik , FT(x)$$ if and only if $$-sqrt2pi , delta'(k) + C , delta(k) = i , FT(x).$$
    $endgroup$
    – md2perpe
    Mar 30 at 16:29















0












$begingroup$


How to find the Fourier transform of $x mapsto x$ using distribution $delta$?



Since $FT(1)=sqrt2pi delta(k)$ then $FT(x cdot 1)=sqrt2pi i delta'(k)$



But also since $1=d/dx (x)$ then $FT(x)=FT(1)/(ik)=delta(k)/(ik)$



Are both of these correct?










share|cite|improve this question











$endgroup$











  • $begingroup$
    You are not really allowed to write $delta(k)/k$ in distribution theory, but the best interpretation if this expressions is $-delta'(k)$.
    $endgroup$
    – md2perpe
    Mar 30 at 16:22











  • $begingroup$
    Your first derivation is correct.
    $endgroup$
    – md2perpe
    Mar 30 at 16:26










  • $begingroup$
    Your second derivation lacks a term $C , delta(k)$: $$sqrt2pi , delta(k) = FT(1) = FT(fracddxx) = ik , FT(x)$$ if and only if $$-sqrt2pi , delta'(k) + C , delta(k) = i , FT(x).$$
    $endgroup$
    – md2perpe
    Mar 30 at 16:29













0












0








0





$begingroup$


How to find the Fourier transform of $x mapsto x$ using distribution $delta$?



Since $FT(1)=sqrt2pi delta(k)$ then $FT(x cdot 1)=sqrt2pi i delta'(k)$



But also since $1=d/dx (x)$ then $FT(x)=FT(1)/(ik)=delta(k)/(ik)$



Are both of these correct?










share|cite|improve this question











$endgroup$




How to find the Fourier transform of $x mapsto x$ using distribution $delta$?



Since $FT(1)=sqrt2pi delta(k)$ then $FT(x cdot 1)=sqrt2pi i delta'(k)$



But also since $1=d/dx (x)$ then $FT(x)=FT(1)/(ik)=delta(k)/(ik)$



Are both of these correct?







fourier-analysis fourier-transform distribution-theory dirac-delta






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Mar 30 at 16:26









Rodrigo de Azevedo

13.2k41962




13.2k41962










asked Mar 30 at 16:15









SørënSørën

1009




1009











  • $begingroup$
    You are not really allowed to write $delta(k)/k$ in distribution theory, but the best interpretation if this expressions is $-delta'(k)$.
    $endgroup$
    – md2perpe
    Mar 30 at 16:22











  • $begingroup$
    Your first derivation is correct.
    $endgroup$
    – md2perpe
    Mar 30 at 16:26










  • $begingroup$
    Your second derivation lacks a term $C , delta(k)$: $$sqrt2pi , delta(k) = FT(1) = FT(fracddxx) = ik , FT(x)$$ if and only if $$-sqrt2pi , delta'(k) + C , delta(k) = i , FT(x).$$
    $endgroup$
    – md2perpe
    Mar 30 at 16:29
















  • $begingroup$
    You are not really allowed to write $delta(k)/k$ in distribution theory, but the best interpretation if this expressions is $-delta'(k)$.
    $endgroup$
    – md2perpe
    Mar 30 at 16:22











  • $begingroup$
    Your first derivation is correct.
    $endgroup$
    – md2perpe
    Mar 30 at 16:26










  • $begingroup$
    Your second derivation lacks a term $C , delta(k)$: $$sqrt2pi , delta(k) = FT(1) = FT(fracddxx) = ik , FT(x)$$ if and only if $$-sqrt2pi , delta'(k) + C , delta(k) = i , FT(x).$$
    $endgroup$
    – md2perpe
    Mar 30 at 16:29















$begingroup$
You are not really allowed to write $delta(k)/k$ in distribution theory, but the best interpretation if this expressions is $-delta'(k)$.
$endgroup$
– md2perpe
Mar 30 at 16:22





$begingroup$
You are not really allowed to write $delta(k)/k$ in distribution theory, but the best interpretation if this expressions is $-delta'(k)$.
$endgroup$
– md2perpe
Mar 30 at 16:22













$begingroup$
Your first derivation is correct.
$endgroup$
– md2perpe
Mar 30 at 16:26




$begingroup$
Your first derivation is correct.
$endgroup$
– md2perpe
Mar 30 at 16:26












$begingroup$
Your second derivation lacks a term $C , delta(k)$: $$sqrt2pi , delta(k) = FT(1) = FT(fracddxx) = ik , FT(x)$$ if and only if $$-sqrt2pi , delta'(k) + C , delta(k) = i , FT(x).$$
$endgroup$
– md2perpe
Mar 30 at 16:29




$begingroup$
Your second derivation lacks a term $C , delta(k)$: $$sqrt2pi , delta(k) = FT(1) = FT(fracddxx) = ik , FT(x)$$ if and only if $$-sqrt2pi , delta'(k) + C , delta(k) = i , FT(x).$$
$endgroup$
– md2perpe
Mar 30 at 16:29










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