Hi;

I really like using the "D" Command because of its format and ease of use, however the command seems to cause me calculation problems - See Attached.

I defined the function f[x,y] and used the function to generate derivatives for both x & y. I then copy and pasted the results into a newly defined function g[x,y] and subsequently calculated the value of g[1,1]

Next I created another function h[x,y] using the same "D" commands that generated the solutions that I copy and pasted into the prior "g" function. The new h[x,y] function give the same results as the prior g[x,y] function however when I use the value of h[1,1], I get a "general" error message stating the "1 is not a valid value".

To further test, I created another function j[x,y] using the Derivative command which does not give an error message and give the expected results.

I use the "D" command a lot and most of the time it seems to give the desired results, and actually prefer it over the Derivative command because the "D" command is faster to use and I like its format better. Currently, I am trying to figure out when I should use the "D" command and when I should use the Derivative command, or whether I should use the "D" command at all.

Please review the attached and let me know if there is a problem in the "D" command code or in the way I am using the command.

Thanks,

Mitch Sandlin