| Fitting plasma waveforms with 10^6 variable combos! [message #93954] |
Tue, 06 December 2016 23:08  |
ted1508
Messages: 1
Registered: December 2016
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Junior Member |
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Hello readers!
This is my first post here and a Hail Mary in a desperate attempt to speed up my IDL code...
I am presenting electric field antenna measurements from dust impacts onto the MAVEN spacecraft around Mars at the AGU conference next week. My code compares these waveforms (600 points) to a theoretical model, of which I have 5 variables, 4 with 10 possible points and 1 with 100 (the higher the resolution the variables the better!).
Problem is, 10^6 loops is a lot to go through. I tried doing it all in massive arrays, and its not much faster (IDL's memory allotment issue versus overhead with for loops)...
At this point I am thinking it would be faster to learn C and recode it from scratch then let this run for a week.
...
Part of the problem is that I am using this function (twice!) for each of the 600 time points:
function fun_ant,time,to,Q,deltat,C_ant,dtprime,tao_ant
tprime=findgen(100)*dtprime
one= exp((-(time-tprime-to)^2)/(2*(deltat)^2))*exp(-(tprime)/tao_ ant)
constant=(-Q/(C_ant*(sqrt(2*!pi)*(deltat))))
equation=constant*Total(one)*dtprime
return, equation
end
The variables which I will be looping through are time, deltat, tao_ant/bod, and Q_ant/bod (for plasma charge recollection to MAVEN's antenna and body respectively)
...
Right now the main procedure runs roughly as follows:
for a = start_a,stop_a-1 do begin ;;; loop through each waveform (there are 5000)
input_max=max(mf_hits[a,*],mf_max_loc) ;;; used to center waveforms later
for ta = 1., 9. do begin ;;;; now all the combinations...
tao_ant = 0.0001*double(ta)
for tb = 1., 9. do begin
tao_bod = 0.0001*double(tb)
print,tb
for dt = 1., 9. do begin
deltat = 0.00001*double(dt)
for qa = 0, 9. do begin
q_ant = 0.000000000001*double(qa)
for qb = 1, 9. do begin
q_bod = 0.000000000001*double(qb)
for n=0,n_elements(new_time)-1 do begin ;;;; and the 600 time points.....
newtime = new_time[n] ;;; the function for this is defined above
pot_ant[n] = fun_ant(newtime,to,q_ant,deltat,C_ant,dtprime,tao_ant)
pot_bod[n] = fun_bod(newtime,to,q_bod,deltat,C_bod,dtprime,tao_bod)
endfor
pot = pot_ant - pot_bod ;;; difference in potential between antenna and spacecraft
Lag_mf = 25 ;;;; how much the 2 waveforms (mf_hits and pot) can shift
similarity=double(max(c_correlate(mf_hits[a,mf_max_loc-103:m f_max_loc+500],pot[0:603],lag_mf)))
if similarity GT best_sim then begin
;;;; save the best variable values
endif
endfor ; qb
endfor ; qa
endfor ; dt
endfor ; tb
endfor ; ta
endfor ; a
...
So theres my problem: I can choose between massive arrays or massive number of for loops, either way resulting in several days of computation.
For those thinking I could step through the values iteratively, there are local 'potential wells' where the similarity value will be higher than the neighbors but still will not be the best fit.
Does anyone have an idea if this code could be sped up by an order of magnitude?
Appreciate all your thoughts!
-Tenacious Ted
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