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
- :
- Solving a Complex Equation in MathCad

Options

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

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

Showing results for

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

11-12-2013
08:45 PM

11-12-2013
08:45 PM

Solving a Complex Equation in MathCad

Trying to solve this equation in mathcad prime, i just cant get the form right, i keep getting an error when I know it should be a simple operation.

It has values S (total distance traveled) and X (horizontal distance traveled) known, trying to solve for the max value of H (height) of an object in parabola projection.

I keep setting the variables, guess for the H variable, and then try to solve the equation using Find(H) or Maximize(H) doesnt work. I'll attach an image of the problem. Any help would be greatly appreciated!

Thanks!

18 REPLIES 18

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

11-12-2013
08:48 PM

11-12-2013
08:48 PM

Re: Solving a Complex Equation in MathCad

Please post your Mathcad worksheet to show what you have done so far.

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

11-12-2013
09:02 PM

11-12-2013
09:02 PM

Re: Solving a Complex Equation in MathCad

Here is what I have

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

11-12-2013
10:19 PM

11-12-2013
10:19 PM

Re: Solving a Complex Equation in MathCad

Why don't you post the sheet? Upper right - Use advanced editor.

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

11-12-2013
10:47 PM

11-12-2013
10:47 PM

Re: Solving a Complex Equation in MathCad

Offhand, it looks like a units mismatch between the first expression and the second. The first expression looks like it results m^2, while everything else results in m

TTFN

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

11-13-2013
05:26 AM

11-13-2013
05:26 AM

Re: Solving a Complex Equation in MathCad

Seems the unit error is in the logarithm. Units inside simplify to meter but you can take the logarithm of a dimensionless expression only.

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

11-14-2013
02:19 AM

11-14-2013
02:19 AM

Re: Solving a Complex Equation in MathCad

Werner Exinger wrote:

One example in Mathcad - Entropy ideal gas calculation:

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

11-13-2013
04:42 AM

11-13-2013
04:42 AM

Re: Solving a Complex Equation in MathCad

Plot please a X-Y graph and see where the curve crosses the x axe

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

11-15-2013
02:59 AM

11-15-2013
02:59 AM

Re: Solving a Complex Equation in MathCad

Samuel…

In your constraints equation, there appears to be a missing operator (plus sign?) between X^2 and 16*H^2 under the square root. In addition, you need to divide the term inside the natural log by meters so that you're taking the ln of a scalar.

Fred

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

11-16-2013
10:26 AM

11-16-2013
10:26 AM

Re: Solving a Complex Equation in MathCad

In addition, you need to divide the term inside the natural log by meters so that you're taking the ln of a scalar.

Or again the formula is false and there is a second missing plus sign between H and the root.

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

11-16-2013
12:26 PM

11-16-2013
12:26 PM

Re: Solving a Complex Equation in MathCad

Hello Werner,

Even if we write the equation with all the signs, there is always no good result.

Always the message on non-compatible units.

Cordially.

Denis

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

11-16-2013
01:45 PM

11-16-2013
01:45 PM

Re: Solving a Complex Equation in MathCad

Even if we write the equation with all the signs, there is always no good result.

Always the message on non-compatible units.

Really?

I just added the two plus signs we wrote about and it works. Not sure if thats the equation Samuel is trying to solve but it looks reasonable. Maybe Sanuel is no longer interested anyway, finally he did not respond until now.

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

11-16-2013
02:30 PM

11-16-2013
02:30 PM

Re: Solving a Complex Equation in MathCad

Hello Werner,

Oops, sorry, it's me, I made a mistake, I put a sign "x" instead of a "+" between H e root.

But also if we do not leave S and X and the last H block, you do not get the solution.

For Samuel, actually it is not income??, It allowed us to study this case and have the same result.

Cordially.

Denis.

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

11-16-2013
04:01 PM

11-16-2013
04:01 PM

Re: Solving a Complex Equation in MathCad

But also if we do not leave S and X and the last H block, you do not get the solution.

Sorry, I don't understand what you mean!?

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

11-17-2013
08:26 AM

11-17-2013
08:26 AM

Re: Solving a Complex Equation in MathCad

Hello Werner,

Here the image representation for the variable S and X inside or outside the box of solution.

Cordially.

Denis

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

11-17-2013
08:42 AM

11-17-2013
08:42 AM

Re: Solving a Complex Equation in MathCad

Mathcads variables are case sensitive!

The solve block should work with X:=15m being inside, too.

Look at the error message - it tells you that X (uppercase) is undefined.

I had the definitions of X and S at the outside because they are no guess values and so have nothing to do with the solvblock itself. They just have to be defined.

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

11-17-2013
04:37 PM

11-17-2013
04:37 PM

Re: Solving a Complex Equation in MathCad

After all it is in any case more versatile and useful to turn the solve block into a function:

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

11-18-2013
01:27 PM

11-18-2013
01:27 PM

Re: Solving a Complex Equation in MathCad

Hello Werner,

Thank you for this very comprehensive demonstration.

I hope it will satisfy the question of Samuel.

Cordially.

Denis

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

11-14-2013
08:35 PM

11-14-2013
08:35 PM

Re: Solving a Complex Equation in MathCad

Hello, Samuel,

Do you have another source for the form of the attachment, because even with other software it is not H.

Do you have any worksheet to send.

As you noted Arbiter, the units are not consistent.

Cordially.

Denis