# langrange interpolation and derivative enquiry

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 March 15, 2006, 19:44 langrange interpolation and derivative enquiry #1 zonexo Guest   Posts: n/a hi, i was reading a paper which uses one-dimensional Lagrange interpolation. Points A,B,D,E,C,P all lie along a line. Functional values at A,B,D,E are known. Dp/d(line)=0 at C. How can one use these info to get the value at P? I thought langrange interpolation only uses functional values. How do I make use of the dp/d(line)=0 at C? Thank you

 March 15, 2006, 23:03 Re: langrange interpolation and derivative enquiry #2 Praveen. C Guest   Posts: n/a You have 5 data. Write a polynomial with 5 degrees of freedom. You get 5 equations for the 5 dof. Solve for them. Then evaluate polynomial at P to get the value there.

 March 16, 2006, 20:19 Re: langrange interpolation and derivative enquiry #3 zonexo Guest   Posts: n/a hi, thanks. r u taking abt polynomial interpolation? ie y=a0+a1*x+a2*x^2+a3*x^3+a4*x^4+a5*x^5 and differentiate to get dy/dx=a1+2*a2*x .... however, i'm referring to lagrange interpolation. the author of the paper has given the hint that dp/dn|_C=a1*p_P+a2*p_B+a3*p_A+a4*p_D+a5*p_E=0 and i'm told to get a1-5 using standard Lagrangian interpolation procedure. So how do I go about it? thanks

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