symvar

Find symbolic variables in symbolic input

Syntax

symvar(s)

symvar(s,n)

Description

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

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

Find Symbolic Variables in Expression

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 Symbolic Variables in Function

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]

Find Default Variable of Expression

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

s — Input

number | vector | matrix | array | symbolic number | symbolic variable | symbolic array | symbolic function | symbolic expression

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

n — Number of variables

integer

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.