How to create Multi Linier regression with matrix

I have a coding to cevelop a newe formulation for Xp.

The main task is to calculate Xp, where in general Xp = Xb/Xc. I want to develop new correlation of XbNew, XcNew and XpNew

I want to modify those formultion by adding some parameters.

So XbNew= a1+a2*X3+a3*X4+a4*X5+a5*-X6

and XcNew=b1+b2*X3+b3*X4+b4*X5+b5*-X6

I want to get new function with those formulation XpNew = 1-(c1*XbNew)*exp(-X2/XbNew)+c1*XbNew

Here my coding

%Input File Input Regression(depth,rd,Vs).txt

file1='Input.txt'

fid=fopen(file1, 'r');

RegAll=fscanf(fid,'%g %g %g %g %g %g %g %g %g', [9,Inf])';

X1 =RegAll(:,1);

X2 =RegAll(:,2); % epicentre distance

X3 =RegAll(:,3); % moment magnitude

X4 =RegAll(:,4); % peak ground surface acceleration

X5 =RegAll(:,5);

X6 =RegAll(:,6);

Xb =RegAll(:,7);

Xc =RegAll(:,8);

Xp =RegAll(:,9);

Alpha=log(Xb);

Betha=log(Xc);

Dist=log(X6);

%prepare data for regression Alpha and Betha

X=[X1 X3 X4 X5 X6];

Y=[Xb];

Z=[Xc];

A=X'*X;

K=inv(X'*X)

B=X'*Y

C=X'*Z

K1=K;

a=K*B

b=K1*C

CBetha=K1*C

for i = 1:length(Const);

XbNew(i)= a1+a2*X3(i)+a3*X4(i)+a4*X5(i)+(a5*-X6(i))

XcNew(i)=b1+b2*X3(i)+b3*X4(i)+b4*X5(i)+(b5*-X6(i));

end

X1=[Const XbNew' XcNew'];

Y1=[Xp];

A1=X1'*X1;

K2=inv(X1'*X1)

c=K2*X1*Y1

%

for k=length(AlphaNew)

XpNew = 1-(c1*XbNew)*exp(-X2/XbNew)+c1*XbNew

end

My question is the value of Xb -XbNew and Xc -XcNew are differs

And why inner matrix between K2, X1 and Y1 are not equal.

How to solve my problem. Thnk you for your kind attention I am appreciat to hear any respond.