Can anyone explain this please ?

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I have a loop that analyses a series of numbers using a sub routine called isLyingInCone and everything is working OK except the speed.

The app takes about 4 hours (that's expected, it crunches through a lot of data) to run and so shortening processes is worthwhile. I'm trying to do this bit by bit and I'm sure there is much to do elsewhere, but I discovered a main culprit was the following IF statement and I cannot understand why the lines below should DOUBLE the analysis time from about 4 to 8 hours. Any idea please?

VB

Dim XTRange As Double
Dim NearAngle As Double
Dim FarAngle As Double
Dim myAngle As Double

If XTRange < 500 Then myAngle = NearAngle Else myAngle = FarAngle 'using this doubles the time ! A select Case instead made little difference

'myAngle = FarAngle 
'If I uncomment the line above it speeds up again - even when leaving the above IF line intact.

If isLyingInCone(Xx, Xy, Xz, Tx, Ty, Tz, Bx, By, Bz, myAngle) = True Then
'here we do the maths
End if

Any help? Im baffled as I'd have thought the IF statement would run anyhow. The difference in time in just adding the

VB

myAngle = FarAngle

line is enormous at 4 - 8 hrs

Thanks

Posted 16-Oct-15 8:28am

SheepRustler

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ZurdoDev 16-Oct-15 14:40pm

Perhaps something like
myAngle = If (XTRange < 500.00, NearAngle, FarAngle)

Note, I did 500.00 instead of 500. I have not tested this but I believe the compiler is converting 500 to a double from an int and that conversion every time may be adding some of your time.

PIEBALDconsult 16-Oct-15 14:51pm

That's one of my thoughts as well.

SheepRustler 16-Oct-15 14:56pm

Sorry I thought Id posted a reply but it doesnt seem to have appeared:

Thanks but no joy, I tried :

Dim Threshold as double = 500.0 (VB strips off the second 00 ?)

and using

myAngle = If (XTRange < Theshold, NearAngle, FarAngle)

but no difference Im afraid....

ZurdoDev 16-Oct-15 14:57pm

And what was the code like before? When it took half the time?

SheepRustler 16-Oct-15 15:00pm

Weirdly exactly the same but with the refining line under the if statement

myAngle = If (XTRange < Theshold, NearAngle, FarAngle)
myAngle = FarAngle 'adding this halves the run time approx

PIEBALDconsult 16-Oct-15 14:50pm

Could part of that be due to an optimizer? If the compiler knows that the if has no effect it could optimize it away? Maybe try compiling with and without optimizations?
Otherwise, I'm baffled as well. The if and the assignments shouldn't be very costly. However, I would try eliminating the assignments and maybe try changing the if to be an integer compare rather than a double compare.

ZurdoDev 16-Oct-15 14:53pm

Another thought, although I don't know enough about compilers to know for sure, but what about putting 500.00 into a const. That way, I believe the compiler allocates memory a single time instead of allocating memory every time this part is called. The compiler may take hard coded numbers and do that internally anyway, I'm not sure.

Tomas Takac 16-Oct-15 15:06pm

I would look on IL code. What is the difference between IF-THEN and SELECT-CASE. Because there is no real reason why one should perform better than the other.

phil.o 16-Oct-15 17:19pm

Could it be possible you get a Double.NaN in your values?
Apart from that, your isLyingInCone(Xx, Xy, Xz, Tx, Ty, Tz, Bx, By, Bz, myAngle) = True statement is redundant ;)

SheepRustler 17-Oct-15 4:53am

Phil,
I dont think so, all the values are (at the end of the run) written from their respective arrays\lists to a couple of text files, I haven't had any NaNs in the results and no exceptions thrown during the number crunching.

Yes, the IsLyinginCone function runs pretty quick.... ;)

SheepRustler 17-Oct-15 4:59am

OK, a bit of an update.
I've added :
Const Thresh = 500.0
with no appreciable difference but what did make a slight (10% in time) different was changing the project compile options from AnyCPU to anything else SLOWED it down by about 10%, as did UNchecking 'Prefer 32 bit'

Checking / unchecking 'Enable Optimisations' in the advanced options made no difference.

Im not sure if this gives any clues, but back to the default values I still get the same massive difference just by adding / removing the commented out line.

myAngle = If(XTRange < Thresh, NearAngle, FarAngle)
'myAngle = FarAngle 'UNcommenting this = twice as fast completion.

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Patrice T · Answer 1 · 2015-10-16T11:48:00

There is no solution with the code you provided.
myAngle is a parameter to what is eating time, so your code have no interest.
You need to run your code on profiler with a small sample of data;
The profiler will tell you where your program is spending time. You will probably see that a small set of lines or a function is eating all the time.
This function is what you need to list with a couple of example parameters, and then it will be possible to understand why it is so long and if it is possible to optimise your code.

This kind of task is usually performed by professional programmer and with full project source code and enough data to see what append.
All is needed because this is an iterative process.
Profiler > see time eater > tweak > profiler > see differences > tweak again ...

The programmer need to fully understand the guilty part of your code in order to optimise it and be really efficient.