It is my understanding that you would like to solve a system of equations in Simulink and perform code generation for the same. The symbolic toolbox does not support C/C++ code generation and hence you cannot use it to solve a system of equations in Simulink. But in case of a normal/accelerated simulation mode this task can be achieved by using the “coder.extrinsic” function. The MATLAB engine executes the calls to functions in the “Symbolic Toolbox”.
You can look at the below code snippets to understand how this function can be used.
You will need to write an external function that uses “solve” to find the solution to the system of equations. The output type must be of “double” format when using this method. As an example, I’ve returned the unknown variable “x1” as “out”.
function out = solveSyms() % add necessary inputs and outputs
syms x1 x2 x3 x4 x5 y1 y2 y3 y4
c = 4; T1 = 80; T2 = 80; T4 = 30; T5 = 30; T6 = 60; T3 = 100; Q1 = 50; Q2 = 50; Q3 = 20; Q4 = 25;
eq1 = Q1 == x1 *(c * T1 - c * y1);
eq2 = Q2 == x2 *(c * T2 - c * y1);
eq3 = Q3 == x3 *(c * y2 - c * T4 );
eq4 = Q4 == x4 *(c * y2 - c * T5 );
eq5 = - x2 *(T2 - y3 ) == x1 *(T1 - y3 );
eq6 = - x3 *(T4 - y4) == + x4 *(T5 - y4);
eq7 = x1 * y1 == - x2 * y1 + x3 * y4 +x4 * y4 + x5 * T6;
eq8 = x1 * y3 == - x2 * y3 + x3 * y2 +x4 * y2 + x5 * T3;
eq9 = x5 == x1 +x2 -x3 - x4;
a=solve(eq1,eq2,eq3,eq4,eq5,eq6,eq7,eq8,eq9,x1, x2, x3, x4, x5, y1, y2, y3, y4);
out = double(a.x1);
end
In your Simulink model call the “coder.extrinsic” function in a MATLAB function block to access the custom function.
function out = fcn(c,T1,T2,T4,T5,T6,T3,Q1,Q2,Q3,Q4)
coder.extrinsic('solveSyms');
out = 0;
out = solveSyms(c,T1,T2,T4,T5,T6,T3,Q1,Q2,Q3,Q4);
You can provide the known values as input to MATLAB function block and define output for each of the unknown variables (x1-x5 and y1-y4) to solve the complete equation using Simulink.
Please have a look at below links for more information.
I hope this helps.
