| Re: Removing if then else loop for efficiency [message #69304 is a reply to message #69298] |
Sun, 10 January 2010 06:46   |
Tom Ashbee
Messages: 3
Registered: January 2010
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Junior Member |
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On Jan 10, 12:06 pm, Tom Ashbee <tlash...@googlemail.com> wrote:
> Hello,
>
> apologies for my newb-ness, but I was hoping I could get some help
> with increasing the efficiency of the following program:
>
> At the moment it is like this
>
> for i=0, N-1 do begin
> for j=0, N-1 do begin
> if i ne j then begin
> ;stuff
> endif else begin
> ;more stuff
> endif
> endfor
> endfor
>
> It's way too slow at the moment, but I gather I can remove one of the
> for loops and the if then else loop but I have no idea how!
>
> Any help would be much appreciated and I can post the full program too
> if it helps. FTR it's the RHS of a Hamiltonian.
>
> Thanks again
OK here's the whole program:
function velocities, t, xyvec
N = 50
R = 5.0
xvec = xyvec(0: N-1)
yvec = xyvec(N: (N*2)-1)
dxvecdt = dblarr(N)
dyvecdt = dblarr(N)
for i = 0, N-1 do begin
dxvecdt(i) = 0.0d
dyvecdt(i) = 0.0d
for j = 0, N-1 do begin
gam = gamma(N, 2.0d, 10.0d)
if i ne j then begin
dxvecdt(i) = dxvecdt(i) + ( gam(j) /(2.0d*!pi))*(yvec(j)-yvec
(i))/((xvec(i)-xvec(j))^2+(yvec(i)-yvec(j))^2) - ( gam(j) /(2.0d*!
pi))*((yvec(j)*R^2)/((xvec(j))^2+(yvec(j))^2)-yvec(i))/((xve c(i)-(xvec
(j)*R^2)/((xvec(j))^2+(yvec(j))^2))^2+(yvec(i)-(yvec(j)*R^2) /((xvec(j))
^2+(yvec(j))^2))^2)
dyvecdt(i) = dyvecdt(i) + ( gam(j) /(2.0d*!pi))*(xvec(i)-xvec
(j))/((xvec(i)-xvec(j))^2+(yvec(i)-yvec(j))^2) - ( gam(j) /(2.0d*!
pi))*(xvec(i)-(xvec(j)*R^2)/((xvec(j))^2+(yvec(j))^2))/((xve c(i)-(xvec
(j)*R^2)/((xvec(j))^2+(yvec(j))^2))^2+(yvec(i)-(yvec(j)*R^2) /((xvec(j))
^2+(yvec(j))^2))^2)
endif else begin
dxvecdt(i) = dxvecdt(i) - ( gam(j) /(2.0d*!pi))*((yvec(j)*R^2)/
((xvec(j))^2+(yvec(j))^2)-yvec(i))/((xvec(i)-(xvec(j)*R^2)/( (xvec(j))
^2+(yvec(j))^2))^2+(yvec(i)-(yvec(j)*R^2)/((xvec(j))^2+(yvec (j))^2))
^2)
dyvecdt(i) = dyvecdt(i) - ( gam(j) /(2.0d*!pi))*(xvec(i)-(xvec
(j)*R^2)/((xvec(j))^2+(yvec(j))^2))/((xvec(i)-(xvec(j)*R^2)/ ((xvec(j))
^2+(yvec(j))^2))^2+(yvec(i)-(yvec(j)*R^2)/((xvec(j))^2+(yvec (j))^2))
^2)
endelse
endfor
endfor
z = [dxvecdt, dyvecdt]
return, z
end
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