MATLAB: Symbolic Toolbox Stuck in Decimal Format

mathsymsymbolicSymbolic Math Toolboxsympref

Best Answer

Your "sympref" settings must have been changed. Restore them to the default with the following:

>> sympref('default');

Now you should get:

>> phi = (1 + sqrt(sym(5)))/2
phi =
5^(1/2)/2 + 1/2

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MATLAB: MeijerG function using MATLAB’s symbolic toolbox

As of R2017b, the function "meijerG" calculates the Meijer G-Function. This function can return either numerical values or symbolic expressions for the Meijer G-Function depending upon the input.

For 'double' inputs, "meijerG" returns a double, as shown below:

>> meijerG(3, [], [], [], 3)

ans =

6.4488

For 'sym' inputs, "meijerG" will return an exact symbolic answer whenever possible. An example is shown below:

>> meijerG(sym(2/5), [], sym(1/2), [], sym(3))

ans =

(2^(4/5)*3^(1/2)*gamma(1/10))/80

The documentation linked below has more details about "meijerG"'s full functionality:

https://www.mathworks.com/help/symbolic/meijerg.html

For prior releases, the symbolic MeijerG function is only available in MuPAD. From MATLAB, it must be evaluated using "evalin", as shown below:

>> y=evalin(symengine, 'simplify(meijerG([[3],[]], [[],[]],3))');

y =

9*exp(-1/3)

Once this command executes, 'y' will contain symbolic MeijerG function for given arguments.

Note that without the call to "simplify", an expression in terms of the MuPAD function "meijerG" may be returned, which will not be understood by MATLAB in further function calls. You can pass this back to "evalin" by first converting it with the "char" function, but this workflow is not recommended.

MATLAB: Is the Symbolic Math Toolbox rounding

When executing sqrt(2*pi)*x, the sqrt(2*pi) is initially calculated as double and so it evaluates to the rounded value, 2.5066. Then, when it is multiplied by the symbolic variable x, it is converted to symbolic form, which is (5644425081792261*x)/2251799813685248. The same is true for exp(5)*x. The exp(5) is first calculated as double and rounded, and then converted to symbolic.

There are two methods to calculate the whole expression as symbolic:

1. Use the "sym" function to declare numeric values as symbolic:

>> y=sqrt(2*sym(pi))*x
>> z=exp(sym(5))*x

2. Use the "str2sym" function which evaluates a string representing a symbolic expression:

>> y=str2sym("sqrt(2*pi)*x")
>> z=str2sym("exp(5)*x")

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Related Solutions

MATLAB: MeijerG function using MATLAB’s symbolic toolbox

MATLAB: Is the Symbolic Math Toolbox rounding

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