;Finds the roots of the quadratic equation a*x^2+b*x+c=0
;
; input
;   a - Quadratic coefficient. May be an array of any shape  
;   b - Linear coefficient. May be array, but must be same shape as a
;   c - Constant coefficient. May be array, but must be same shape as a
; output keywords
;   d - Discriminant. Same shape as a. Wherever there is a negative value in this
;       array, there are no real roots, and root1 and root2 will have NaN in
;       the corresponding elements
;   root1 - Root found by using + sign in quadratic formula
;   root2 - Root found by using - sign in quadratic formula
pro quadratic_formula,a,b,c,d=d,root1=root1,root2=root2
  d=b^2-4*a*c
  root1=(-B+sqrt(D))/(2*A);
  root2=(-B-sqrt(D))/(2*A);
end