POLYNOMIAL Approximation to a Function

[Anousheh]

Hello everyone,

Please look at the attached MathCad worksheet.

I would like to generate a suitable (cubic) polynomial to Ki"zero"(alpha) function and compare it with the actual one.

I guess, MathCad can do this automatically.

Thank you so much for the time and help.

Regards,

Anousheh

[RogerYeh]

Hmmmm, well, you can use the POLYFIT function:

If you change the x-values over which you're fitting, you get different looking curves:

[Anousheh]

Hello Roger,

Thank you so much.

This is the range I am interested in:

As it can be seen, it is not a good fit in this range.

This is what I need from MathCad: I have generated this manually in EXCEL.

One other thing: I need to have the actual POLYNOMIAL function (like one highlighted above) for publication purposes.

Regards,

Anousheh

[RogerYeh · Accepted solution]

There were some errors in appending the images. I only see one (the first one).

In regards to the coefficients, use POLYFITC:

[Anousheh]

Hello Roger,

Thanks again. I really appreciate this.

I have sorted the problem. Please see bellow:

The polynomial fits perfectly. Thanks again.

This solves my problem. Thanks and regards,

Anousheh

[Werner_E]

You may try simple regress an go for the coefficients

[Anousheh]

Hello Werner,

Yet, another beautiful worksheet. Very nice and helpful. I shall use this as a REFERENCE for future use.

One question: how do we expand this for multi-variable functions?

Thank you and regards,

Anousheh

[Werner_E]

One question: how do we expand this for multi-variable functions?

Thank you and regards,

Anousheh

Getting the coefficients is a bit more work for multi variable functions and uttilizes one or two small programs. Fortunately thats covered very well in the help. Look for regress and follow the link on the bottom to the appropriate quicksheet. My wisdom stems from there 😉

[Anousheh]

Hello Werner,

Thank you for your input.

Appreciate your time and help.

All the best,

Anousheh