equation as an output

can you make an equation as an output of a function?

like, for example I want to make a function that has the output of f =@(x) a*x^2 %a is the number that we input

Answer 1

[Ayush Modi]

Hi Clara,

Yes, you can create a function in MATLAB that returns another function (a function handle to be precise) as its output. Here is the example code to get you started:

a = 10 % Sample input

a = 10

bb = createQuadraticFunction(a) % bb stores the function handle

bb = function_handle with value:
    @(x)a*x.^2

bb(10) % Checking the use of function handle

ans = 1000

function f = createQuadraticFunction(a)
    % This function returns a quadratic function f(x) = a*x^2
    f = @(x) a * x.^2;
end

Refer to the following MathWorks documentation for more information on function handles:

https://www.mathworks.com/help/matlab/matlab_prog/creating-a-function-handle.html

Answer 2

[Walter Roberson]

syms a x
expr = a*x^2

expr = 

try
    f = matlabFunction(expr, 'vars', x)
catch ME
    warning(ME.message)
end

Warning: Free variable 'a' must be included in 'Vars' value.

So you have the problem that a is needed but it is not input to the function.

On the other hand,

a = 9.8;
expr = a*x^2

expr = 

f = matlabFunction(expr, 'vars', x)

f = function_handle with value:
    @(x)x.^2.*(4.9e+1./5.0)

This has the disadvantage that the value of a is expanded in-line

There is no way with the Symbolic Toolbox to generate a function referring to a captured variable by name