| Re: do I need this IF statement? [message #43238] |
Thu, 24 March 2005 07:29 |
Benjamin Luethi
Messages: 22
Registered: December 2004
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Junior Member |
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Hi again,
Just realized that d = SQRT(x(INDGEN(M))^2 + y(INDGEN(N))^2) isn't giving
you the desired matrix (it's just a vector). But
d = SQRT( (x(INDGEN(M))#replicate(1,N))^2
+ (y(INDGEN(N))#replicate(1,M))^2 )
should work...
Ben
On Thu, 24 Mar 2005 16:05:52 +0100, Benjamin Luethi <luethi@phim.unibe.ch>
wrote:
> Hi,
>
> No, if I understand your program correctly: You're adding all image
> values that are closer than 3sigma (to be precise you weigh each value
> with p before adding).
>
> You can achieve the same with the following 4 lines:
>
> d = SQRT(x(INDGEN(M))^2 + y(INDGEN(N))^2)
> usable = d lt 3.*sigma
>
> p = some_function( x(INDGEN(M)), y(INDGEN(N)) )
>
> profile = TOTAL( usable * p * image )
>
> If a position (x(i),y(j)) is further away than 3sigma then usable[i,j]
> is zero and thus the image value is not added to the profile.
>
> I don't know what you do in v = v1 + vr(i,indx). It doesn't make sense
> since v is overwritten in each loop and never used anyway...
>
> And note:
> if y has N elements then you can write y instead of y(INDGEN(N)).
>
> This is a solution to this case - there might be some cases however,
> where it's not that easy or even impossible.
>
> Ben
>
>
>
>
>
>
> On 24 Mar 2005 02:07:01 -0800, Margrethe <margrethewold@hotmail.com>
> wrote:
>
>>
>> I find that in some cases I really need an IF statement to make sure
>> that I don't address some arrays with index -1. In the example below I
>> have vectorized the inner loop over j, but have kept the loop over i.
>> Is there a way to avoid the IF statement? Grateful for help! -Margrethe
>>
>> FOR i=0,N-1 DO BEGIN
>>
>> d = sqrt ( x(i) ^2 + y (INDGEN(N)) ^2 )
>> indx = WHERE ( d LT 3.*sigma, ct )
>>
>> IF (ct GT 0) THEN BEGIN
>>
>> v = v1 + vr (i,indx)
>> p = some_function ( x(i), y(indx) )
>> profile = profile + TOTAL ( p * image(i,indx) )
>>
>> ENDIF
>>
>> ENDFOR
>>
>
>
>
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| Re: do I need this IF statement? [message #43241 is a reply to message #43238] |
Thu, 24 March 2005 07:05  |
Benjamin Luethi
Messages: 22
Registered: December 2004
|
Junior Member |
|
|
Hi,
No, if I understand your program correctly: You're adding all image
values that are closer than 3sigma (to be precise you weigh each value
with p before adding).
You can achieve the same with the following 4 lines:
d = SQRT(x(INDGEN(M))^2 + y(INDGEN(N))^2)
usable = d lt 3.*sigma
p = some_function( x(INDGEN(M)), y(INDGEN(N)) )
profile = TOTAL( usable * p * image )
If a position (x(i),y(j)) is further away than 3sigma then usable[i,j]
is zero and thus the image value is not added to the profile.
I don't know what you do in v = v1 + vr(i,indx). It doesn't make sense
since v is overwritten in each loop and never used anyway...
And note:
if y has N elements then you can write y instead of y(INDGEN(N)).
This is a solution to this case - there might be some cases however,
where it's not that easy or even impossible.
Ben
On 24 Mar 2005 02:07:01 -0800, Margrethe <margrethewold@hotmail.com> wrote:
>
> I find that in some cases I really need an IF statement to make sure
> that I don't address some arrays with index -1. In the example below I
> have vectorized the inner loop over j, but have kept the loop over i.
> Is there a way to avoid the IF statement? Grateful for help! -Margrethe
>
> FOR i=0,N-1 DO BEGIN
>
> d = sqrt ( x(i) ^2 + y (INDGEN(N)) ^2 )
> indx = WHERE ( d LT 3.*sigma, ct )
>
> IF (ct GT 0) THEN BEGIN
>
> v = v1 + vr (i,indx)
> p = some_function ( x(i), y(indx) )
> profile = profile + TOTAL ( p * image(i,indx) )
>
> ENDIF
>
> ENDFOR
>
--
Using Opera's revolutionary e-mail client: http://www.opera.com/m2/
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| Re: do I need this IF statement? [message #43246 is a reply to message #43241] |
Thu, 24 March 2005 04:48 |
David Fanning
Messages: 11724
Registered: August 2001
|
Senior Member |
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Margrethe writes:
> I find that in some cases I really need an IF statement to make sure
> that I don't address some arrays with index -1. In the example below I
> have vectorized the inner loop over j, but have kept the loop over i.
> Is there a way to avoid the IF statement? Grateful for help! -Margrethe
>
> FOR i=0,N-1 DO BEGIN
>
> d = sqrt ( x(i) ^2 + y (INDGEN(N)) ^2 )
> indx = WHERE ( d LT 3.*sigma, ct )
>
> IF (ct GT 0) THEN BEGIN
>
> v = v1 + vr (i,indx)
> p = some_function ( x(i), y(indx) )
> profile = profile + TOTAL ( p * image(i,indx) )
>
> ENDIF
>
> ENDFOR
JD has me totally intimidated about making sweeping generalizations,
but I'm going to state emphatically that you NEED the IF statement.
We'll see if that turns out to be true. :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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