Note: This page has been translated by MathWorks. Please click here

To view all translated materals including this page, select Japan from the country navigator on the bottom of this page.

To view all translated materals including this page, select Japan from the country navigator on the bottom of this page.

This example shows you how to solve parameterized algebraic equations using the Symbolic Math Toolbox™.

To solve algebraic equations symbolically, use the `solve`

function. The solve function can provide complete information about all solutions of an equation, even if there are infinitely many, by introducing a parameterization. It can also provide information under which conditions these solutions are valid. To obtain this information, set the option ReturnConditions to true.

Solve the equation `sin(C*x) = 1`

. Specify `x`

as the variable to solve for. The `solve`

function handles `C`

as a constant. Provide three output variables for the solution, the newly generated parameters in the solution, and the conditions on the solution.

syms C x eq = sin(C*x) == 1; [solx, params, conds] = solve(eq, x, 'ReturnConditions', true)

solx =

params =

conds =

To verify the solution, substitute the solution into the equation using `subs`

. To work on under the assumptions in `conds`

for the rest of this example, use `assume`

. Test the solution using `isAlways`

. The `isAlways`

function returns logical `1`

(`true`

) indicating that the solution always holds under the given assumptions.

SolutionCorrect = subs(eq, x, solx)

SolutionCorrect =

assume(conds) isAlways(SolutionCorrect)

ans = 1

To obtain one solution out of the infinitely many solutions, find a value of the parameters `params`

by solving the conditions `conds`

for the parameters; do not specify the ReturnConditions option. Substitute this value of `k`

into the solution using `subs`

to obtain a solution out of the solution set.

k0 = solve(conds, params)

k0 =

subs(solx, params, k0)

ans =

To obtain a parameter value that satisfies a certain condition, add the condition to the input to `solve`

. Find a value of the parameter greater than `99/4`

and substitute in to find the solution.

k1 = solve([conds, params > 99/4], params)

k1 =

subs(solx, params, k1)

ans =

To find a solution in a specified interval, you can solve the original equation with the inequalities that specify the interval.

`[solx1, params1, conds1] = solve([eq, x > 2, x < 7], x, 'ReturnConditions', true)`

solx1 =

params1 =

conds1 =

Alternatively, you can also use the existing solution, and restrict it with additional conditions. Note that while the condition changes, the solution remains the same. The `solve`

function expresses `solx`

and `solx1`

with different parameterizations, although they are equivalent.

`[~, ~, conds2] = solve(x == solx, x < 7, x > 2, x, 'ReturnConditions', true)`

conds2 =

Obtain those parameter values that satisfy the new condition, for a particular value of the constant C:

conds3 = subs(conds2, C, 5)

conds3 =

solve(conds3, params)

ans =

Was this topic helpful?