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Field of numbers

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Dom::Numerical is the field of numbers.

Dom::Numerical is the domain of numbers represented by one of the kernel domains DOM_INT, DOM_RAT, DOM_FLOAT, or DOM_COMPLEX.

Dom::Numerical is of category Cat::Field due to pragmatism. This domain actually is not a field because bool(1.0 = float(3) / float(3)) returns FALSE, for example.

Elements of Dom::Numerical are usually not created explicitly. However, if one creates elements using the usual syntax, it is checked whether the input expression can be converted into a number (see below).

This means that Dom::Numerical is a façade domain which creates elements of domain type DOM_INT, DOM_RAT, DOM_FLOAT or DOM_COMPLEX. Every system function dealing with numbers can be applied, and computations in this domain are performed efficiently.

Dom::Numerical has no normal representation, because 0 and 0.0 both represent zero.

Viewed as a differential ring, Dom::Numerical is trivial. It only contains constants.

If x is a constant arithmetical expression such as sin(2) or PI + 2, the system function float is applied to convert x into a floating-point approximation.

An error message is issued if the result of this conversion is not of domain type DOM_FLOAT or DOM_COMPLEX.


Example 1

Dom::Numerical contains numbers of the domains DOM_INT, DOM_RAT, DOM_FLOAT and DOM_COMPLEX:

Dom::Numerical(2), Dom::Numerical(2/3), 
Dom::Numerical(3.141), Dom::Numerical(2 + 3*I)

Constant arithmetical expressions are converted into a real and complex floating-point number, respectively, i.e., into an element of the domain DOM_FLOAT or DOM_COMPLEX (see the function float for details):

Dom::Numerical(exp(5)), Dom::Numerical(sin(2/3*I) + 3)

Note that the elements of this domain are elements of kernel domains, there are no elements of the domain type Dom::Numerical!

An error message is issued for non-constant arithmetical expressions:

Error: The arguments are invalid. [Dom::Numerical::new]

Example 2

Dom::Numerical is regarded as a field, and it therefore can be used as a coefficient ring of polynomials or as a component ring of matrices, for example.

We create the domain of matrices of arbitrary size (see Dom::Matrix) with numerical components:

MatN := Dom::Matrix(Dom::Numerical)

Next we create a banded matrix, such as:

A := MatN(4, 4, [-PI, 0, PI], Banded)

and a row vector with four components as a 1 ×4 matrix:

v := MatN([[2, 3, -1, 0]])

Vector-matrix multiplication can be performed with the standard operator * for multiplication:

v * A

Finally we compute the determinant of the matrix A, using the function det:




An arithmetical expression



is zero.


expand all

Mathematical Methods


See the function D for details and further calling sequences.

diff(a, x)

See the function diff for details and further calling sequences.



Conversion Methods


If x is of the domain type DOM_INT, DOM_RAT, DOM_FLOAT or DOM_COMPLEX, x is returned.

Otherwise float(x) is computed and the result is returned, if it is of the domain type DOM_FLOAT or DOM_COMPLEX. If it is not, FAIL is returned.

convert_to(a, T)

If the conversion fails, FAIL is returned.

It currently handles the following domains for T: DOM_INT, Dom::Integer, DOM_RAT, Dom::Rational, DOM_FLOAT, Dom::Float and DOM_COMPLEX.

testtype(a, T)

This method is called from the function testtype.

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