Complementary polynomial space

  • Thread starter Thread starter Mindscrape
  • Start date Start date
  • Tags Tags
    Polynomial Space
Mindscrape
Messages
1,854
Reaction score
1
Let V = P^{(4)} denote the space of quartic polynomials, with the L^2 inner product

<p,q>= \int_{-l}^l p(x)q(x)dx

Let W = P^2 be the subspace of quadratic polynomials.
a) Write down the conditions that a polynomial p \in P^{(4)} must satisfy in order to belong to the orthogonal complement Wperp.
b) Find a basis for and the dimension of Wperp.
c) Find an orthogonal basis for Wperp.

The first part just goes off the definition of a complementary subspace.
W_{perp} = (q(x) = a + bx + cx^2 + dx^3 + ex^4 | <p,1>=<p,x>=<p,x^2>=0)

It looks like the second part wants me to actually do the calculation, but that looks like a lot of work to multiply it out. Is that really what it is asking?

The last part should be easy, because I can just take the basis from part b) and apply the Gram-Schmidt method.
 
Last edited:
Physics news on Phys.org
What is 'a lot of work to multiply out'? It's just monomials times a polynomial integrated over [-1,1]. You get three conditions on a,b,c,d,e. It doesn't get too much more straightforward than that.
 
Prove $$\int\limits_0^{\sqrt2/4}\frac{1}{\sqrt{x-x^2}}\arcsin\sqrt{\frac{(x-1)\left(x-1+x\sqrt{9-16x}\right)}{1-2x}} \, \mathrm dx = \frac{\pi^2}{8}.$$ Let $$I = \int\limits_0^{\sqrt 2 / 4}\frac{1}{\sqrt{x-x^2}}\arcsin\sqrt{\frac{(x-1)\left(x-1+x\sqrt{9-16x}\right)}{1-2x}} \, \mathrm dx. \tag{1}$$ The representation integral of ##\arcsin## is $$\arcsin u = \int\limits_{0}^{1} \frac{\mathrm dt}{\sqrt{1-t^2}}, \qquad 0 \leqslant u \leqslant 1.$$ Plugging identity above into ##(1)## with ##u...
Back
Top