- #1

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## Main Question or Discussion Point

I have this function (1-6*x^2)^-1 and i want to polynomial interpolation (lagrange and spline) in 21 equidistant points [-1,1]

I made this function

x =linspace(-1,1,21);

y = (1-6*x^2)^-1;

z=[-1:0.01:1]

c=polyfit(x,y,20)

p=polyval(c,z)

s=spline(x,y,z)

plot(z,(1-6*x^2)^-1, z, p, z, s);

and I receive error at y = (1-6*x^2)^-1;

if I use a function with x only instead of x^2 it works.

How can I fix it?

I made this function

x =linspace(-1,1,21);

y = (1-6*x^2)^-1;

z=[-1:0.01:1]

c=polyfit(x,y,20)

p=polyval(c,z)

s=spline(x,y,z)

plot(z,(1-6*x^2)^-1, z, p, z, s);

and I receive error at y = (1-6*x^2)^-1;

if I use a function with x only instead of x^2 it works.

How can I fix it?