(35S) HP35s - Medical applications

[mchris]

The second medical stuff I post is a CKD-EPI equation. The CKD-EPI equation is for calculating the estimated GFR of a patient with chronic kidney failure. It is a complicated equation with 4 piecewise functions and 2 min/max functions.

The HP35s lacks both. It is easy to write a program to emulate them but I wanted to write the whole thing as an equation. Here comes linear algebra for the rescue. The equation has a term k. k is a function itself with a term 0.9 if it is a man or 0.7 if it is a woman. I wanted to write 1 for a man, 2 for a woman, 1 for non-black, 2 for black. There must be a system of equations 1x+y=0.9 and 2x+y=0.7 to solve to replace the piecewise function k. The same goes for term α and for the last two terms (1.018 if male, 1.159 if black). And finally I replaced min(a,b) and max(a,b) functions with a+b-abs(a-b) and a+b+abs(a-b) (thanks to this forum).
The final equation is:
141*((1+C/(S*-0,2+1,1)-abs(1-C/(S*-0,2+1,1)))/2)^(S*0,082-0,493)*((1+C/(S*-0,2+1,1)+abs(1-C/(S*-0,2+1,1)))/2)^-1,209*0,993^A*(S*0,018+0,982)*(R*0,159+0,841)