topic Re: reply to BEN ABOUT THE RESISTIVITY PROGRAM in LabVIEW

reply to BEN ABOUT THE RESISTIVITY PROGRAM

utp — Fri, 20 Sep 2002 16:20:29 GMT

Ben,
Following is the code of the Resistivity measurement program that i had posted a question about.
Look at the loop in the following position in the program::
Outermost TRUE frame
Frame 2
Frame 2
Look at the loop taking input from the Q control on the front panel.Also the input is taken from another array , F .The program first calculates Qa and then searches array Q for the closest value and then remembers the index at which the closest value was found and from the same position in another array (f)gets a value Fa .Fb is calculated similarly.
This takes foreveR(BUT IS NOT WRONG-JUST TAKES TOO LONG , MY BOSS SAYS EARLIER IT DIDNT TAKE SO LONG)
SO KINDLY HELP
REGARDS
UT
PAL

Re: reply to BEN ABOUT THE RESISTIVITY PROGRAM

Ben — Fri, 20 Sep 2002 18:16:07 GMT

If you are sure the case you mentioned is where all the time is being spent, you may want to experiment with using

"Threshold 1d array" and/or "interpolate 1d array". These VI are faster than doing expilicitly.

What has changed since when it didn't take so long?

Are you using more memory thatn before?

Are you GPIB devices on different cables or farther away?

Do you have any idea how big the arrays in questions are?

Ben

Re: reply to BEN ABOUT THE RESISTIVITY PROGRAM

allaba — Sat, 21 Sep 2002 07:05:58 GMT

Re: reply to BEN ABOUT THE RESISTIVITY PROGRAM

allaba — Sat, 21 Sep 2002 07:05:59 GMT

"utp" schrieb im Newsbeitrag
news:506500000008000000A35C0000-1031838699000@exchange.ni.com...
> Ben,
> Following is the code of the Resistivity measurement program that i
> had posted a question about.
> Look at the loop in the following position in the program::
> Outermost TRUE frame
> Frame 2
> Frame 2
> Look at the loop taking input from the Q control on the front
> panel.Also the input is taken from another array , F .The program
> first calculates Qa and then searches array Q for the closest value
> and then remembers the index at which the closest value was found and
> from the same position in another array (f)gets a value Fa .Fb is
> calculated similarly.
> This takes foreveR(BUT IS NOT WRONG-JUST TAKES TOO LONG , MY BOSS SAYS
> EARLIER IT DIDNT TAKE SO LONG)
> SO KINDLY HELP
> REGARDS
> UTPAL

Utpal,

concerning the code you mention, Ben's answer is correct, it is a sort of
interpolation which is done in your code.
The calculation is done in an extremely inefficient manner in the code. I
compared it with an optimised code and found that the speed differed by a
factor of 10. The absolute numbers were 12 ?sec for the optimised code and
117 ?sec for the code in your program. But this was under Labview 6.1 on a
2.3 GHz pentium, and you talked about LV 4 (on a probably much slower
machine).
HOWEVER, the calculation speed depends on the value of the input number Qa,
since a long array (roughly 6000 elements) has to be searched through. For
Qa values close to 1 (which you probably have for a "well behaved" van der
Pauw sample) the code in your program takes twice as long as the numbers
above indicate (whereas for a Qa of, say, bigger than 5000 the speed is much
faster).

Now suppose your PC is a factor of 10 slower and suppose further that LV 4
is another factor of 10 slower than LV 6.1 (it is doing lots of 'array
subset' operations in your code) and considering further that the algorithm
is performed 4 times in your program, we might expect a speed of 2 x 10 x 10
x 4 = 800 slower than the numbers above, i.e. 800 x 117 ?sec which is appr,
0.1 sec.

Therefor I believe that the awfully long times you report are not due to
this (admittedly very inefficient piece of) math code.

I attach 2 png pictures, showing
a) the optimised code
b) how to convert the two big array constants in your code into a form
suitable for the optimised code

You should run b) only once of course and then store array [(Q,f)] in your
program.

If you have access to Labview 6.0 or 6.1, I could also send you the code
directly.

-Franz

[Attachment Calculate interpolated f(Q)d.png, see below]

[Attachment Make Q,f arrayd.png, see below]