SE: filter to SallenKey

[B,A]=cheby1(3,1,10*10^6*2*pi,'s');

%3rd order sallen key
syms Ra Rb Rc Rd Re Ca Cb Cc
M=1+Rd/Re;
num= M/(Ra*Rb*Rc*Ca*Cb*Cc);

den1=1;
den2=(1/(Ra*Ca)+1/(Rb*Ca)+1/(Rb*Cb)+(1-M)/(Rc*Cc)+1/(Rc*Cb));
den3=((Cc*Rc+Ra*Cc+Rb*Cc+Ca*Ra+(1-M)*(Ra+Rb)*Cb)/(Ra*Rb*Rc*Ca*Cb*Cc));
den4=(1/(Ra*Rb*Rc*Ca*Cb*Cc));
As = [den2 den3 den4];

Mdesired = 5;
denom = A - As;
numer = B(end) - num;
Mcon  = M - Mdesired;

%%
x = solve(denom,numer,Mcon,Ra,Rb,Rc,Rd,Re)