Documentation

This is machine translation

Translated by Microsoft
Mouseover text to see original. Click the button below to return to the English verison of the page.

Note: This page has been translated by MathWorks. Please click here
To view all translated materals including this page, select Japan from the country navigator on the bottom of this page.

eq

Define equation

In previous releases, eq in some cases evaluated equations involving only symbolic numbers and returned logical 1 or 0. To obtain the same results as in previous releases, wrap equations in isAlways. For example, use isAlways(A == B).

Syntax

A == B
eq(A,B)

Description

A == B creates a symbolic equation. You can use that equation as an argument for such functions as solve, assume, ezplot, and subs.

eq(A,B) is equivalent to A == B.

Input Arguments

A

Number (integer, rational, floating-point, complex, or symbolic), symbolic variable or expression, or array of numbers, symbolic variables or expressions.

B

Number (integer, rational, floating-point, complex, or symbolic), symbolic variable or expression, or array of numbers, symbolic variables or expressions.

Examples

Define and Solve Equation

Solve this trigonometric equation. Define the equation by using the relational operator ==.

syms x
solve(sin(x) == cos(x), x)
ans =
pi/4

Plot Symbolic Equation

Plot the equation $\sin(x^2) - \sin(y^2)$. Define the equation by using the == operator.

syms x y
fimplicit(sin(x^2) == sin(y^2))

Test Equality of Symbolic Expressions

Test the equality of two symbolic expressions by using isAlways.

syms x
isAlways(x + 1 == x + 1)
ans =
  logical
   1
isAlways(sin(x)/cos(x) == tan(x))
ans =
  logical
   1

Test Equality of Symbolic Matrices

Check the equality of two symbolic matrices.

A = sym(hilb(3));
B = sym([1, 1/2, 5; 1/2, 2, 1/4; 1/3, 1/8, 1/5]);
isAlways(A == B)
ans =
  3×3 logical array
     1     1     0
     1     0     1
     1     0     1

If you compare a matrix and a scalar, then == expands the scalar into a matrix of the same dimensions as the input matrix.

A = sym(hilb(3));
B = sym(1/2);
isAlways(A == B)
ans =
  3×3 logical array
     0     1     0
     1     0     0
     0     0     0

Related Examples

More About

collapse all

Tips

  • Calling == or eq for non-symbolic A and B invokes the MATLAB® eq function. This function returns a logical array with elements set to logical 1 (true) where A and B are equal; otherwise, it returns logical 0 (false).

  • If both A and B are arrays, then these arrays must have the same dimensions. A == B returns an array of equations A(i,j,...) == B(i,j,...)

  • If one input is scalar and the other is an array, then == expands the scalar into an array of the same dimensions as the input array. In other words, if A is a variable (for example, x), and B is an m-by-n matrix, then A is expanded into m-by-n matrix of elements, each set to x.

See Also

| | | | | |

Introduced in R2012a

Was this topic helpful?