1537 Views 9 Replies Latest reply: Feb 19, 2012 2:10 PM by A.Non
5 posts since
Feb 12, 2012
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## Explicit function definition

Hello,

I am quite new to Mathcad. What I want to do is to define a function explicitly (i.e., as pairs of x - y or x - f(x) values), not analitically (through a formula). Does anyone know wether that is possible or not? I am using Mathcad 14 and I searched the user guide, provided examples and tutorials, but couldn't find anything related to this subject. I even tried to do that myself, by improvising, but without any success.

Moreover, if it's possible to define a function explicitly, could one calculate definite integrals on it afterwards? (I know that is easy if the function is defined analitically).

Best regards,

Marius

• 4,522 posts since
Dec 3, 2008
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Feb 12, 2012 11:40 PM (in response to ptc-4457992)
Re: Explicit function definition

Yes I believe it is possible, but I'm not sure exactly what your after.

Could you provide an example and post the worksheet?

Mike

• 2,398 posts since
Sep 26, 2010
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Feb 12, 2012 11:42 PM (in response to ptc-4457992)
Re: Explicit function definition

Hello!

Provide a screenshot of what you want.

• 1,771 posts since
Nov 28, 2006
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Feb 13, 2012 3:46 AM (in response to ptc-4457992)
Re: Explicit function definition

Given an x,y data set there are several ways to proceed; the choice depends on the data and what you want to do.  With a dense and complete data set you can use numerical integration techniques.  You can curve fit the data--find a function that approximates the data closely, and use the built-in integration schemes for manipulation.

• 10,396 posts since
May 11, 2010
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Feb 13, 2012 6:54 AM (in response to ptc-4457992)
Re: Explicit function definition

You need to create an interpolating function. The most general solution is a cubic spline, but it's not always appropriate. Without seeing the data it's hard to say much more.

• 10,396 posts since
May 11, 2010
Currently Being Moderated
Feb 19, 2012 2:10 PM (in response to ptc-4457992)
Re: Explicit function definition

We don't need the same reply four times. It's just as easy to read one reply four times as it is to read four replies

I don’t need any curve fitting, interpolation function or any other kind of approximation.

All numerical integration is approximate. The attached is a very general, and usually accurate, approach.

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