Why?

[Douglas Clark]

Zhang,

I think the problem is that 'define'  works by stepping through z and t (if they are varying).

e.g.
set z 1 4
define a=diff(u,z)
will try to use diff at z=1, then diff at z=2,..etc. Since diff cannot take a difference if only given one value (one level), it returns the error message.

If you just want to display the difference, that will work OK
eg
d diff(u,z)
but define will not work.

If you need to use define, you'll have to devise a way of working round this.

Doug

>>> zdr1168 at YAHOO.COM 23/08/2005 12:57:10 >>>
 Sir ,

 I want to use CDIFF function to carry out vertical difference. But
 when I use the funtion CDIFF like:
 'define a=diff(u,z)'
 there occur errors like:

Operation Error:  Error from cdiff function
   Error ocurred at column 1
 DEFINE error:  Invalid expression.
 Error from CDIFF:  Specified dimension non varying
 Why?

 The function DIFF can not carry out vertical difference?

 Help me please!



Yours,
Zhang



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