Get Help

Turn on suggestions

Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.

Showing results for

- Community
- :
- PTC Mathcad
- :
- PTC Mathcad
- :
- It seems only a math problem, but I can't understa...

Options

- Subscribe to RSS Feed
- Mark Topic as New
- Mark Topic as Read
- Float this Topic for Current User
- Bookmark
- Subscribe
- Printer Friendly Page

Auto-suggest helps you quickly narrow down your search results by suggesting possible matches as you type.

Showing results for

Highlighted

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Notify Moderator

07-01-2014
10:49 AM

07-01-2014
10:49 AM

Just Like the pictures and the worksheet bellow, I have only changed the y's assignment position, but the result is different! So I hope someone could help me. Thanks a lot.

Solved! Go to Solution.

1 ACCEPTED SOLUTION

Accepted Solutions

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Notify Moderator

07-01-2014
11:43 AM

07-01-2014
11:43 AM

It is a problem that needs differentiation by parts

Your function is d/dx of a(x)*b(x) so the result should be: (d/dx a(x) ) *b(x) + a(x) * (d/dx b(x))

Unfortunately if you define f(x,y) mathcad is assuming that these parameters are independant

When later you let mathcad know that y=x^5 then it substitutes that into the result it already had,

but information is lost & you get an incorrect answer.

2 REPLIES 2

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Notify Moderator

07-01-2014
11:43 AM

07-01-2014
11:43 AM

It is a problem that needs differentiation by parts

Your function is d/dx of a(x)*b(x) so the result should be: (d/dx a(x) ) *b(x) + a(x) * (d/dx b(x))

Unfortunately if you define f(x,y) mathcad is assuming that these parameters are independant

When later you let mathcad know that y=x^5 then it substitutes that into the result it already had,

but information is lost & you get an incorrect answer.

- Mark as New
- Bookmark
- Subscribe
- Subscribe to RSS Feed
- Permalink
- Email to a Friend
- Notify Moderator

07-01-2014
12:42 PM

07-01-2014
12:42 PM

Re: It seems only a math problem, but I can't understand it.

……but information is lost ……

OK, I should tell mathcad the informations in order. Really! I've forgotten the difference of relationship between x and y in different assignment position. Thank you very much!

Top Tags