# symvar

Find symbolic variables in symbolic input

## Syntax

``symvar(s)``
``symvar(s,n)``

## Description

example

````symvar(s)` returns a vector of all symbolic variables in `s`. The variables are in alphabetical order with uppercase letters preceding lowercase letters.```

example

````symvar(s,n)` chooses the `n` symbolic variables in `s` that are alphabetically closest to `x` and returns them in alphabetical order. If `s` is a symbolic function, `symvar(s,n)` returns the input arguments of `s` before other variables in `s`.```

## Examples

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Find all symbolic variables in an expression. `symvar` returns the variables in alphabetical order.

```syms wa wb yx ya sum = wa + wb + ya + yx; symvar(sum)```
```ans = [ wa, wb, ya, yx]```

Find the first three symbolic variables in an expression. `symvar` chooses variables that are alphabetically closest to `x` and returns them in alphabetical order.

```syms a x y b f = a*x^2/(sin(3*y-b)); symvar(f,3)```
```ans = [ b, x, y]```

Find all symbolic variables in this function. For a symbolic function, `symvar` returns the function inputs before other variables.

```syms x y a b f(x,y) = a*x^2/(sin(3*y-b)); symvar(f) ```
```ans = [ x, y, a, b]```
```g(x,y) = 1; symvar(g)```
```ans = [ x, y]```

Find the first three symbolic variables in `f`.

`symvar(f,3)`
```ans = [ x, y, b]```

When a symbolic function, such as `solve`, needs to find the default independent variable in symbolic, the function uses `symvar`. Find the default independent variable for symbolic expressions.

```syms v z g = v + z; symvar(g,1)```
```ans = z```
```syms aaa aab g = aaa + aab; symvar(g,1)```
```ans = aaa```
```syms X1 x2 xa xb g = X1 + x2 + xa + xb; symvar(g,1)```
```ans = x2```

When differentiating, integrating, substituting, or solving equations, MATLAB® uses the variable returned by `symvar(s,1)` as a default variable. For a symbolic expression or matrix, `symvar(s,1)` returns the variable closest to `x`. For a function, `symvar(s,1)` returns the first input argument of `s`.

## Input Arguments

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Input, specified as a number, vector, matrix, or array, or a symbolic number, variable, array, function, or expression.

Number of variables, specified as an integer or `Inf`. If `n` exceeds the number of variables in `s`, then `symvar` returns the number of variables in `s`.

## Tips

• `symvar` treats the constants `pi`, `i`, and `j` as variables.

• If there are no symbolic variables in `s`, `symvar` returns the empty vector.

## Algorithms

When `symvar` sorts the symbolic variables alphabetically, all uppercase letters have precedence over lowercase: 0 1 ... 9 A B ... Z a b ... z.

## Version History

Introduced in R2008b