function getThetas() {
	/* eslint-disable no-invalid-this */
	var Theta;
	var val;
	var d;
	var k;

	Theta = matrix( [ this.D, this.K ] );
	for ( d = 0; d < this.D; d++ ) {
		for ( k = 0; k < this.K; k++ ) {
			val = ( this.nd.get( d, k ) + this.alpha ) /
				( this.ndSum[ d ] + ( this.K*this.alpha ) );
			Theta.set( d, k, val );
		}
	}
	return Theta;
}
Get theta matrix. Its rows correspond to document distributions over topics.

@private
@returns {Matrix} theta parameter matrix