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L
Ln31-Visitor
1-Visitor
April 6, 2020
Solved

Plotting failed. Replace complex values and NaNs by real numbers.

  • April 6, 2020
  • 2 replies
  • 7816 views

Hello,

 

I am new to MathCad. I plotted the freefall equation and solved for x and z. Then I would like to plot the velocity, so x' and z' but get the error: "replace with complex values and NaNs by real numbers". It shouldn't have complex values and NaNs, I have checked the odesolve syntax, the time step and the units, but still can't find the mistake.

Would appreciate help! The file is attached.

Thanks in advance!

 

Ln

Best answer by Werner_E

You may consider using a simple range variable for t rather than the vector you used.

Werner_E_0-1586184582497.png

I am not quite sure why Prime has problems with the way you had set up the sheet - it should work OK. But Prime seems to have problems with the combination of the vector t and the derivative operator. We may call it a bug.

Another way around this problem/bug is to define the derivatives as separate functions and use these:

Werner_E_1-1586184932221.png

 

 

2 replies

L
LucMeekes23-Emerald IV
23-Emerald IV
April 6, 2020

There's something weird going on in your sheet.

The two functions x1'(t) and z1'(t) are not defined which I think is what causes the error message for your plot.

But I would have expected an error message at the definition of v1(t), which uses those two undefined functions.

 

Luc

L
Ln31-VisitorAuthor
1-Visitor
April 6, 2020

Hey Luc,

 

I thought it is enough to define the u0 and v0, and when solving x and z, it should calculate x'(t) and z'(t). If I insert a single value for t, I also get a plausible answer.

Do you have an idea why I get these results as well as the plot v1(t)?

W
Werner_E25-Diamond IAnswer
25-Diamond I
April 6, 2020

You may consider using a simple range variable for t rather than the vector you used.

Werner_E_0-1586184582497.png

I am not quite sure why Prime has problems with the way you had set up the sheet - it should work OK. But Prime seems to have problems with the combination of the vector t and the derivative operator. We may call it a bug.

Another way around this problem/bug is to define the derivatives as separate functions and use these:

Werner_E_1-1586184932221.png

 

 

L
Ln31-VisitorAuthor
1-Visitor
April 6, 2020

ok, thank you Werner!

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