# Where did I go wrong

• April 9th 2012, 08:24 AM
southprkfan1
Where did I go wrong
Suppose I have an odd, increasing function h with h(0)=0 and an unknown increasing function f(D), f(0)=0.

Let:

$\phi(h(f(D))*h(f(D))*h'(f(D))*f'(D)=D$

where $\phi$ is the standard normal pdf

From the above equation, we can see that D spans the real line and the when the RHS is > 0 so is the LHS.

But, I can rewrite the above equation as:

$\frac{-\partial\phi(h(f(D))}{\partial{D}}=D$

$\implies 0.5*D^2=-\phi(h(f(D))$

which does not make sense since the LHS is > 0 and the RHS is < 0