Using LINEST for trig functions

[MichaelP]

Hi, please forgive I am a little bit of a newcommer to using LINEST in excel but I have now mastered using it to do a x3 polynomial regressession fit and that works fine.

The trouble is the data I want to fit is really sinusoidal and I would like a sine function fit. I have seen some references that seem to say this is possible to do in LINEST but I do not see how to code the function instruction.

What I want to fit is something like y= a sin(bx) + c

Could anybody confirm that this is possible to do with LINEST and help me with how I code the function command.

Many thanks

[shg]

LINEST will only do regression that is linear in its coefficients. Your function is not linear in b.

[MichaelP]

Thanks shg, that clarifies.

If I accept that I can not do the b in above formulae how would I code to cater for y= a Sin(x) + b?

Thanks again.

[shg]

=linest(y, sin(x))

[MichaelP]

Thanks shg, that was quick! OK as simple as that it assumes the a & b as though it were a simple linear. Many thanks I think I get the picture now.

[shg]

it assumes the a & b as though it were a simple linear.

LINEST doesn't assume anything -- it can't tell that the values it receives are the result of a function applied.