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symvar

Find symbolic variables in symbolic expression, matrix, or function

Syntax

symvar(s)
symvar(s,n)

Description

symvar(s) returns a vector containing all the symbolic variables in s 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 sorts them alphabetically before returning them. If s is a symbolic function, symvar(s,n) returns the input arguments of s before other free variables in s.

Input Arguments

s

Symbolic expression, matrix, or function.

n

Integer or Inf. If n exceeds the number of variables in s, then symvar(s,n) is equivalent to symvar(s,m) where m is the number of variables in s.

Examples

Find all symbolic variables in this sum.

syms wa wb wx yx ya yb
symvar(wa + wb + wx + ya + yb + yx)
ans =
[ wa, wb, wx, ya, yb, yx]

Find all symbolic variables in this function.

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

Find the first three symbolic variables in f. For a symbolic function, symvar with two arguments returns the function inputs before other variables.

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

Find the first three symbolic variables in an expression. For a symbolic expression or matrix, symvar chooses variables alphabetically closest to x and sorts them alphabetically.

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

Find the default symbolic variable of these 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

Tips

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

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

  • 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.

Algorithms

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

Introduced in R2008b

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