User input not being plugged into the equation

Hello,

Something tells me there's a simple solution to my problem, but i can't seem to figure it out. Here's my code:

prompt={'Enter value for R_bd: ', 'Enter value for R_ad: ', 'Enter value for R_ae: ', 'Enter value for R_be: '};
answer=inputdlg(prompt);
x1 = str2num(answer{1});
x2 = str2num(answer{2});
x3 = str2num(answer{3});
x4 = str2num(answer{4});
equ1='x1-R1*(R2+R3+R4)/(R1+R2+R3+R4)';
equ2='x2-R2*(R1+R3+R4)/(R1+R2+R3+R4)';
equ3='x3-R3*(R1+R2+R4)/(R1+R2+R3+R4)';
equ4='x4-R4*(R1+R2+R3)/(R1+R2+R3+R4)';
sol=solve(equ1,equ2,equ3,equ4);
R1=sol.R1
R2=sol.R2
R3=sol.R3
R4=sol.R4

My issue with this code is, the number being entered by the user (say you input 3 for all the four answers) is not being plugged in equ1 - equ4 to generate an answer.

When I write the code like this it works just fine:

equ1='3-R1*(R2+R3+R4)/(R1+R2+R3+R4)';
equ2='3-R2*(R1+R3+R4)/(R1+R2+R3+R4)';
equ3='3-R3*(R1+R2+R4)/(R1+R2+R3+R4)';
equ4='3-R4*(R1+R2+R3)/(R1+R2+R3+R4)';
sol=solve(equ1,equ2,equ3,equ4)
R1=sol.R1
R2=sol.R2
R3=sol.R3
R4=sol.R4

But the values can vary which is why I need the user to input the values. What am I doing wrong?

Thank you in advance.

[Thamer]

Nvm, I figured it out. Thanks

Answer 1

[Walter Roberson]

Switch to the formulation I showed in http://www.mathworks.co.uk/matlabcentral/answers/84057#comment_163152

[Thamer]

Thank you Walter, I will add tha to my code to generate only the positive answer.

[Thamer]

Btw to get back on subject, would you be able to help me with my inquiry above? How can I incorporate a user input command to work with the code above? (refer to the example on the question)

[Walter Roberson]

prompt={'Enter value for R_bd: ', 'Enter value for R_ad: ', 'Enter value for R_ae: ', 'Enter value for R_be: '};
answer=inputdlg(prompt);
x1 = str2num(answer{1});
x2 = str2num(answer{2});
x3 = str2num(answer{3});
x4 = str2num(answer{4});
syms R1 R2 R3 R4 positive
equ1=x1-R1*(R2+R3+R4)/(R1+R2+R3+R4);
equ2=x2-R2*(R1+R3+R4)/(R1+R2+R3+R4);
equ3=x3-R3*(R1+R2+R4)/(R1+R2+R3+R4);
equ4=x4-R4*(R1+R2+R3)/(R1+R2+R3+R4);
sol=solve(equ1,equ2,equ3,equ4);
R1=sol.R1
R2=sol.R2
R3=sol.R3
R4=sol.R4

[Thamer]

Thanks!