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eq

Define equation

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 . 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```

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

Topics

Introduced in R2012a

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