difalm

Description
difalm performs arithmetic operations or linear combinations on $a_{{\ell}m}$. difmap can swap the amplitudes and phases between two sets of $a_{{\ell}m}$. It can shift the phases by a constant value, or multiply/divide $a_{{\ell}m}$ by given vectors $v({\ell})$.

Examples

• difalm alm1.fits alm2.fits -o alm.out.fits
  performs simple subtraction: $a^{1}_{{\ell}m}-a^{2}_{{\ell}m}$ from files ' alm1.fits' and ' alm2.fits' and outputs to file ' alm.out.fits'.

• difalm -cd 1.5 alm.fits -o alm.out.fits
  divides the $a_{{\ell}m}$ from file ' alm.fits' by a factor of 1.5 and outputs to ' alm.out.fits'.

• difalm -sum alm1.fits alm2.fits -lmax 20 -o alm.out.fits
  adds 2 sets of $a_{{\ell}m}$ from files ' alm1.fits' and ' alm2.fits', and outputs the result up to ${\ell}=20$ in ' alm.out.fits'.

• difalm alm.fits -vm cl.ls -o alm.out.fits
  multiplies the $a_{{\ell}m}$ at each ${\ell}$ from file ' alm1.fits' with the value $v({\ell})$ from the ASCII file ' cl.ls' and outputs to ' alm.out.fits'.