Documentation |
Convert set of linear equations to matrix form
[A,b] =
equationsToMatrix(eqns,vars)
[A,b] =
equationsToMatrix(eqns)
A = equationsToMatrix(eqns,vars)
A = equationsToMatrix(eqns)
[A,b] = equationsToMatrix(eqns,vars) converts eqns to the matrix form. Here eqns must be linear equations in vars.
[A,b] = equationsToMatrix(eqns) converts eqns to the matrix form. Here eqns must be a linear system of equations in all variables that symvar finds in these equations.
A = equationsToMatrix(eqns,vars) converts eqns to the matrix form and returns only the coefficient matrix. Here eqns must be linear equations in vars.
A = equationsToMatrix(eqns) converts eqns to the matrix form and returns only the coefficient matrix. Here eqns must be a linear system of equations in all variables that symvar finds in these equations.
eqns |
Vector of equations or equations separated by commas. Each equation is either a symbolic equation defined by the relation operator == or a symbolic expression. If you specify a symbolic expression (without the right side), equationsToMatrix assumes that the right side is 0. Equations must be linear in terms of vars. |
vars |
Independent variables of eqns. You can specify vars as a vector. Alternatively, you can list variables separating them by commas. Default: Variables determined by symvar |
A |
Coefficient matrix of the system of linear equations. |
b |
Vector containing the right sides of equations. |
Convert this system of linear equations to the matrix form. To get the coefficient matrix and the vector of the right sides of equations, assign the result to a vector of two output arguments:
syms x y z [A, b] = equationsToMatrix([x + y - 2*z == 0, x + y + z == 1,... 2*y - z + 5 == 0], [x, y, z])
A = [ 1, 1, -2] [ 1, 1, 1] [ 0, 2, -1] b = 0 1 -5
Convert this system of linear equations to the matrix form. Assigning the result of the equationsToMatrix call to a single output argument, you get the coefficient matrix. In this case, equationsToMatrix does not return the vector containing the right sides of equations:
syms x y z A = equationsToMatrix([x + y - 2*z == 0, x + y + z == 1,... 2*y - z + 5 == 0], [x, y, z])
A = [ 1, 1, -2] [ 1, 1, 1] [ 0, 2, -1]
Convert this linear system of equations to the matrix form without specifying independent variables. The toolbox uses symvar to identify variables:
syms s t [A, b] = equationsToMatrix([s - 2*t + 1 == 0, 3*s - t == 10])
A = [ 1, -2] [ 3, -1] b = -1 10
Find the vector of variables determined for this system by symvar:
X = symvar([s - 2*t + 1 == 0, 3*s - t == 10])
X = [ s, t]
Convert X to a column vector:
X = X.'
X = s t
Verify that A, b, and X form the original equations:
A*X == b
ans = s - 2*t == -1 3*s - t == 10
If the system is only linear in some variables, specify those variables explicitly:
syms a s t [A, b] = equationsToMatrix([s - 2*t + a == 0, 3*s - a*t == 10], [t, s])
A = [ -2, 1] [ -a, 3] b = -a 10
You also can specify equations and variables all together, without using vectors and simply separating each equation or variable by a comma. Specify all equations first, and then specify variables:
syms x y [A, b] = equationsToMatrix(x + y == 1, x - y + 1, x, y)
A = [ 1, 1] [ 1, -1] b = 1 -1
Now change the order of the input arguments as follows. equationsToMatrix finds the variable y, then it finds the expression x — y + 1. After that, it assumes that all remaining arguments are equations, and stops looking for variables. Thus, equationsToMatrix finds the variable y and the system of equations x + y = 1, x = 0, x - y + 1 = 0:
[A, b] = equationsToMatrix(x + y == 1, x, x - y + 1, y)
A = 1 0 -1 b = 1 - x -x - x - 1
If you try to convert a nonlinear system of equations, equationsToMatrix throws an error:
syms x y [A, b] = equationsToMatrix(x^2 + y^2 == 1, x - y + 1, x, y)
Error using symengine (line 56) Cannot convert to matrix form because the system does not seem to be linear.