Fortran calculate distance of many points to fixed point

Question

Is there a more elegant and concise way to calculate the distances between a set of points and a fixed point than doing this?

real, dimension(3, numPoints) :: points
real, dimension(3) :: source
real, dimension(numPoints) :: r

r = sqrt((points(1,:) - source(1))**2 + &
         (points(2,:) - source(2))**2 + 
         (points(3,:) - source(3))**2)

I tried

r = sqrt(sum((points - source)**2,1))

but this - unsurprisingly - does not work.

Answer 1

If you have a bang-up-to-date compiler, one which implements the intrinsic functions added to Fortran in the 2008 revision, the following expression might satisfy your ideas of elegance and concision for the computation of one distance:

r(1) = norm2(points(:,1)-source)

If you don't have a bang-up-to-date compiler you'll probably find either that your compiler has a non-standard function for the L2 norm or that you have a library hanging around that implements it.

I don't have Fortran on this machine, so upranking this to a one-liner that calculates the distances of all the points from source, I leave that to the interested reader. But I wouldn't sniff at the obvious solution of looping over all the points in turn.

EDIT: OK, here's a one-liner, untested

r = norm2(points-spread(source,dim=1,ncopies=numpoints),dim=2)