# Interpolation / Curve fitting / Empirical formula

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satendra kumar 2011년 11월 16일
Hii, I have an Eq.- M=A[P^a]*[Q^b]*[R^c] From experiments the value of M,P,Q,R is known to me. Now i need to find the value of A,a,b,c... Can anyone tell me how to solve this problem

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### 답변 (1개)

Andrew Newell 2011년 11월 17일
Take the logarithms of both sides, so you have a linear regression problem. How you solve that depends on whether you have the Statistics Toolbox.
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satendra kumar 2011년 11월 17일
Thanks for your ans, but In my prblm the power may be anything not like 1,2,3,4. The values of a,b,c can be anything as .5,.6 so I think its not a linear regression problem.
Kindly send me some more suggestions
Andrew Newell 2011년 11월 17일
If you take the logarithms, you get:
log(M) = log(A) + a*log(P) + b*log(Q) + c*log(R).
That's a linear equation, equivalent to
y = r +a*x1 + b*x2 +c*x3.
That's a linear equation in the variables y=log(M), x1=log(P), etc., and there is certainly no requirement that r, a, b and c be integers.

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