| CHECK_MATH and exp() [message #31890] |
Mon, 26 August 2002 16:15  |
jeyadev
Messages: 78
Registered: February 1995
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Member |
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Could someone please explain this:
WAVE> junk = check_math(1,0)
WAVE> print, junk
0
WAVE> y = exp(-9.2^2)
WAVE> print, y, check_math(1,0)
1.74307e-37 0
WAVE> y = exp(-9.3^2)
WAVE> print, y, check_math(1,0)
2.74074e-38 0
WAVE> y = exp(-9.4^2)
% Program caused arithmetic error: Floating underflow
% Program caused arithmetic error: Floating illegal operand
WAVE> print, y, check_math(1,0)
4.22418e-39 0
I first ran into the problem in a set of loops, and narrowed down
the
% Program caused arithmetic error: Floating illegal operand
error to a call to the exp() function. A little fooling around
resulted in getting to the above. It appears that when the argument
reaches -9.4^2, the underflow occurs, but I cannot understand the
"illegal operand". Also, why does CHECK_MATH() not catch the
underflow.
And, now for more:
WAVE> .run
- for i=90,100 do begin
- x = i/10.0
- y = exp(-x^2)
- print, x, y, check_math(1,0)
- endfor
- end
% Compiled module: $MAIN$.
9.00000 6.63968e-36 128
9.10000 1.08661e-36 128
9.20000 1.74307e-37 128
9.30000 2.74074e-38 128
% Program caused arithmetic error: Floating underflow
% Program caused arithmetic error: Floating illegal operand
9.40000 4.22418e-39 160
% Program caused arithmetic error: Floating underflow
% Program caused arithmetic error: Floating illegal operand
9.50000 6.38150e-40 160
% Program caused arithmetic error: Floating underflow
% Program caused arithmetic error: Floating illegal operand
9.60000 9.44966e-41 160
% Program caused arithmetic error: Floating underflow
% Program caused arithmetic error: Floating illegal operand
9.70000 1.37159e-41 160
% Program caused arithmetic error: Floating underflow
% Program caused arithmetic error: Floating illegal operand
9.80000 1.95201e-42 160
% Program caused arithmetic error: Floating underflow
% Program caused arithmetic error: Floating illegal operand
9.90000 2.71852e-43 160
% Program caused arithmetic error: Floating underflow
% Program caused arithmetic error: Floating illegal operand
10.0000 3.78351e-44 160
Again, I can see the problem for x > 9.3. But, what is the
CHECK_MATH() doing? First, it seems to say that there is an
"floating point operand error", and then it is that *plus*
and underflow. What is the "floating point operand error"
that the code 128 is indicating?
I am running PV-WAVE CL Version 6.01 (sun4 solaris sparc)
on a Sun Ultra 10 under Solaris 8.
thanks
--
Surendar Jeyadev jeyadev@wrc.xerox.bounceback.com
Remove 'bounceback' for email address
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| Re: CHECK_MATH and exp() [message #31926 is a reply to message #31890] |
Fri, 30 August 2002 12:36  |
jeyadev
Messages: 78
Registered: February 1995
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Member |
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In article <3D6CDC8E.DB526253@saicmodis.com>,
James Kuyper <kuyper@saicmodis.com> wrote:
Thanks for your reply ......
> Surendar Jeyadev wrote:
>>
>> Could someone please explain this:
> ...
>> WAVE> y = exp(-9.4^2)
>> % Program caused arithmetic error: Floating underflow
>> % Program caused arithmetic error: Floating illegal operand
>
> I only get the first message, not the second.
The begining of the differences .....!
> Since the exp() call occurred before the last interactive prompt, it
> doesn't count. Instead, try the following:
>
> IDL> y = exp(-9.4^2) & print,check_math(-1)
> % Program caused arithmetic error: Floating underflow
> 32
And I get
WAVE> y = exp(-9.4^2) & print,check_math(-1)
% Program caused arithmetic error: Floating underflow
% Program caused arithmetic error: Floating illegal operand
160
>> I am running PV-WAVE CL Version 6.01 (sun4 solaris sparc)
>> on a Sun Ultra 10 under Solaris 8.
Obviously, it is something to do with ....
> I am running idl 5.4 on an SGI machine running IRIX,
.... PV-Wave. Not sure if it is to do with the Sun version,
though.
thanks, anyway,
--
Surendar Jeyadev jeyadev@wrc.xerox.bounceback.com
Remove 'bounceback' for email address
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| Re: CHECK_MATH and exp() [message #31965 is a reply to message #31890] |
Wed, 28 August 2002 07:22 |
James Kuyper
Messages: 425
Registered: March 2000
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Senior Member |
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Surendar Jeyadev wrote:
>
> Could someone please explain this:
...
> WAVE> y = exp(-9.4^2)
> % Program caused arithmetic error: Floating underflow
> % Program caused arithmetic error: Floating illegal operand
I only get the first message, not the second.
> ... Also, why does CHECK_MATH() not catch the
> underflow.
Because, as the documentation says:
"No errors detected since the last interactive prompt or call to
CHECK_MATH".
Since the exp() call occurred before the last interactive prompt, it
doesn't count. Instead, try the following:
IDL> y = exp(-9.4^2) & print,check_math(-1)
% Program caused arithmetic error: Floating underflow
32
check_math() wasn't really intended for use at the command line; you get
immediate notification of errors when working interactively, so it isn't
needed.
> And, now for more:
>
> WAVE> .run
> - for i=90,100 do begin
> - x = i/10.0
> - y = exp(-x^2)
> - print, x, y, check_math(1,0)
> - endfor
> - end
> % Compiled module: $MAIN$.
> 9.00000 6.63968e-36 128
> 9.10000 1.08661e-36 128
> 9.20000 1.74307e-37 128
> 9.30000 2.74074e-38 128
> % Program caused arithmetic error: Floating underflow
> % Program caused arithmetic error: Floating illegal operand
> 9.40000 4.22418e-39 160
...
I get:
% Compiled module: $MAIN$.
9.00000 6.63968e-36 0
9.10000 1.08661e-36 0
9.20000 1.74307e-37 0
9.30000 2.74074e-38 0
% Program caused arithmetic error: Floating underflow
9.40000 0.00000 32
> I am running PV-WAVE CL Version 6.01 (sun4 solaris sparc)
> on a Sun Ultra 10 under Solaris 8.
I am running idl 5.4 on an SGI machine running IRIX,
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