function variable$1(x, dtype, name, constraint) {
	  return new LayerVariable(x, dtype, name, true, constraint);
	}
Create a Variable.
@param x The initial value of the `Variable`.
@param dtype optional, the type of the variable.
@param name optional, the name of the variable, default provided by
Variable.
@param constraint optional, a constraint to be applied after every update.
@return The newly instantiated `Variable`.