# Standard Deviation

Normal distribution standard deviation.

## Usage

``````var stdev = require( '@stdlib/math/base/dists/normal/stdev' );
``````

#### stdev( mu, sigma )

Returns the standard deviation for a normal distribution with parameters `mu` (mean) and `sigma` (standard deviation).

``````var y = stdev( 2.0, 1.0 );
// returns 1.0

y = stdev( -1.0, 4.0 );
// returns 4.0
``````

If provided `NaN` as any argument, the function returns `NaN`.

``````var y = stdev( NaN, 1.0 );
// returns NaN

y = stdev( 0.0, NaN );
// returns NaN
``````

If provided `sigma <= 0`, the function returns `NaN`.

``````var y = stdev( 0.0, 0.0 );
// returns NaN

y = stdev( 0.0, -1.0 );
// returns NaN
``````

## Examples

``````var randu = require( '@stdlib/random/base/randu' );
var stdev = require( '@stdlib/math/base/dists/normal/stdev' );

var sigma;
var mu;
var y;
var i;

for ( i = 0; i < 10; i++ ) {
mu = ( randu()*10.0 ) - 5.0;
sigma = randu() * 20.0;
y = stdev( mu, sigma );
console.log( 'µ: %d, σ: %d, Var(X;µ,σ): %d', mu.toFixed( 4 ), sigma.toFixed( 4 ), y.toFixed( 4 ) );
}
``````