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Since the type of a variable may change during the execution of a
program, it can be necessary to do type checking at run-time. Doing this
also allows you to change the behavior of a function depending on the
type of the input. As an example, this naive implementation of `abs`

returns the absolute value of the input if it is a real number, and the
length of the input if it is a complex number.

function a = abs (x) if (isreal (x)) a = sign (x) .* x; elseif (iscomplex (x)) a = sqrt (real(x).^2 + imag(x).^2); endif endfunction

The following functions are available for determining the type of a variable.

- Built-in Function:
**isnumeric***(*`x`) Return true if

`x`is a numeric object, i.e., an integer, real, or complex array.Logical and character arrays are not considered to be numeric.

**See also:**isinteger, isfloat, isreal, iscomplex, islogical, ischar, iscell, isstruct, isa.

- Built-in Function:
**islogical***(*`x`) - Built-in Function:
**isbool***(*`x`) Return true if

`x`is a logical object.

- Built-in Function:
**isfloat***(*`x`) Return true if

`x`is a floating-point numeric object.Objects of class double or single are floating-point objects.

- Built-in Function:
**isreal***(*`x`) Return true if

`x`is a non-complex matrix or scalar.For compatibility with MATLAB, this includes logical and character matrices.

- Built-in Function:
**iscomplex***(*`x`) Return true if

`x`is a complex-valued numeric object.**See also:**isreal, isnumeric, islogical, ischar, isfloat, isa.

- Built-in Function:
**ismatrix***(*`a`) Return true if

`a`is a 2-D array.**See also:**isscalar, isvector, iscell, isstruct, issparse, isa.

- Function File:
**isvector***(*`x`) Return true if

`x`is a vector.A vector is a 2-D array where one of the dimensions is equal to 1. As a consequence a 1x1 array, or scalar, is also a vector.

- Function File:
**isrow***(*`x`) Return true if

`x`is a row vector 1xN with non-negative N.

- Function File:
**iscolumn***(*`x`) Return true if

`x`is a column vector Nx1 with non-negative N.

- Function File:
**issquare***(*`x`) Return true if

`x`is a square matrix.

- Function File:
**issymmetric***(*`A`) - Function File:
**issymmetric***(*`A`,`tol`) Return true if

`A`is a symmetric matrix within the tolerance specified by`tol`.The default tolerance is zero (uses faster code).

Matrix

`A`is considered symmetric if`norm (`

.`A`-`A`.', Inf) / norm (`A`, Inf) <`tol`**See also:**ishermitian, isdefinite.

- Function File:
**ishermitian***(*`A`) - Function File:
**ishermitian***(*`A`,`tol`) Return true if

`A`is Hermitian within the tolerance specified by`tol`.The default tolerance is zero (uses faster code).

Matrix

`A`is considered symmetric if`norm (`

.`A`-`A`', Inf) / norm (`A`, Inf) <`tol`**See also:**issymmetric, isdefinite.

- Function File:
**isdefinite***(*`A`) - Function File:
**isdefinite***(*`A`,`tol`) Return 1 if

`A`is symmetric positive definite within the tolerance specified by`tol`or 0 if`A`is symmetric positive semidefinite. Otherwise, return -1.If

`tol`is omitted, use a tolerance of`100 * eps * norm (`

`A`, "fro")**See also:**issymmetric, ishermitian.

- Function File:
**isbanded***(*`A`,`lower`,`upper`) Return true if

`A`is a matrix with entries confined between`lower`diagonals below the main diagonal and`upper`diagonals above the main diagonal.`lower`and`upper`must be non-negative integers.

- Function File:
**isdiag***(*`A`) Return true if

`A`is a diagonal matrix.

- Function File:
**istril***(*`A`) Return true if

`A`is a lower triangular matrix.A lower triangular matrix has nonzero entries only on the main diagonal and below.

- Function File:
**istriu***(*`A`) Return true if

`A`is an upper triangular matrix.An upper triangular matrix has nonzero entries only on the main diagonal and above.

- Function File:
**isprime***(*`x`) Return a logical array which is true where the elements of

`x`are prime numbers and false where they are not.A prime number is conventionally defined as a positive integer greater than 1 (e.g., 2, 3, …) which is divisible only by itself and 1. Octave extends this definition to include both negative integers and complex values. A negative integer is prime if its positive counterpart is prime. This is equivalent to

`isprime (abs (x))`

.If

`class (`

is complex, then primality is tested in the domain of Gaussian integers (http://en.wikipedia.org/wiki/Gaussian_integer). Some non-complex integers are prime in the ordinary sense, but not in the domain of Gaussian integers. For example,`x`)*5 = (1+2i)*(1-2i)*shows that 5 is not prime because it has a factor other than itself and 1. Exercise caution when testing complex and real values together in the same matrix.Examples:

isprime (1:6) ⇒ [0, 1, 1, 0, 1, 0]

isprime ([i, 2, 3, 5]) ⇒ [0, 0, 1, 0]

Programming Note:

`isprime`

is appropriate if the maximum value in`x`is not too large (< 1e15). For larger values special purpose factorization code should be used.Compatibility Note:

`matlab`does not extend the definition of prime numbers and will produce an error if given negative or complex inputs.

If instead of knowing properties of variables, you wish to know which variables are defined and to gather other information about the workspace itself, see Status of Variables.

Previous: Promotion and Demotion of Data Types, Up: Numeric Data Types [Contents][Index]