Minimize the number of tensor components according...

by: Maple

Minimize the number of tensor components according to its symmetries
(and relabel, redefine or count the number of independent tensor components)

The nice development described below is work in collaboration with Pascal Szriftgiser from Laboratoire PhLAM, Université Lille 1, France, used in the Mapleprimes post Magnetic traps in cold-atom physics

A new keyword in Define  and Setup : minimizetensorcomponents, allows for automatically minimizing the number of tensor components taking into account the tensor symmetries. For example, if a tensor with two indices in a 4D spacetime is defined as antisymmetric using Define with this new keyword, the number of different tensor components will be exactly 6, and the elements of the diagonal are automatically set equal to 0. After setting this keyword to true with Setup , all subsequent definitions of tensors automatically minimize the number of components while using this keyword with Define  makes this minimization only happen with the tensors being defined in the call to Define .

Related to this new functionality, 4 new Library routines were added: MinimizeTensorComponents, NumberOfIndependentTensorComponents, RelabelTensorComponents and RedefineTensorComponents

Example:

 >

Define an antisymmetric tensor with two indices

 >
 (1.1)

Although the system knows that  is antisymmetric, you need to use Simplify to apply the (anti)symmetry

 >
 (1.2)

 >
 (1.3)

so by default the components of  do not automatically reflect the (anti)symmetry; likewise

 >
 (1.4)
 >
 (1.5)

and computing the array form of we do not see the elements of the diagonal equal to zero nor the lower-left triangle equal to the upper-right triangle but for a different sign:

 >
 (1.6)

On the other hand, this new functionality, here called minimizetensorcomponents, makes the symmetries of the tensor be explicitly reflected in its components.

There are three ways to use it. First, one can minimize the number of tensor components of a tensor previously defined. For example

 >
 (1.7)

After this, both (1.2) and (1.3) are automatically equal to 0 without having to use Simplify

 >
 (1.8)
 >
 (1.9)

And the output of TensorArray  in (1.6) becomes equal to (1.7).

NOTE: in addition, after using minimizetensorcomponents in the definition of a tensor, say F, all the keywords implemented for Physics tensors are available for F:

 >
 (1.10)
 >
 (1.11)
 >
 (1.12)
 >
 (1.13)

Alternatively, one can define a tensor, specifying that the symmetries should be taken into account to minimize the number of its components passing the keyword minimizetensorcomponents to Define .

Example:

Define a tensor with the symmetries of the Riemann  tensor, that is, a tensor of 4 indices that is symmetric with respect to interchanging the positions of the 1st and 2nd pair of indices and antisymmetric with respect to interchanging the position of its 1st and 2nd indices, or 3rd and 4th indices, and define it minimizing the number of tensor components

 >
 (1.14)

We now have

 >
 (1.15)
 >
 (1.16)
 • One can always retrieve the symmetry properties in the abstract notation used by the Define command using the new , its output is ordered, first the symmetric then the antisymmetric properties

 >
 (1.17)
 • After making the symmetries explicit (and also before that), it is frequently useful to know the number of independent components of a given tensor. For this purpose you can use the new

 >
 (1.18)

and besides taking into account the symmetries, in the case of the Riemann  tensor, after taking into account the first Bianchi identity this number of components is further reduced to 20.

A third way of using the new minimizetensorcomponents functionality is using Setup , so that, automatically, every subsequent definition of tensors with symmetries is performed minimizing the number of its components using the indicated symmetries

Example:

 >
 (1.19)

So from hereafter you can define tensors taking into account their symmetries explicitly and without having to include the keyword  at each definition

 >
 (1.20)

 >
 (1.21)
 • Two new related functionalities are provided via  and , the first one to have the number of tensor components directly reflected in the names of the components, the second one to redefine only one of these components
 >
 (1.22)

Suppose now we want to make one of these components equal to 1, say

 >
 (1.23)

This nice development is work in collaboration with Pascal Szriftgiser from Laboratoire PhLAM, UMR CNRS 8523, Université Lille 1, F-59655, France.

 >

Edgardo S. Cheb-Terrab
Physics, Differential Equations and Mathematical Functions, Maplesoft

An example of the kinds of worksheets that i make...

by: Maple

Hello,

I study mainly subjects that fall under umbrella of number theory, but i have specified a little further in the worksheet. This is really a request for assistance, because in as much as i have met so many brilliant people online via social media etc,  I would always love to meet more, and especially ones who are more experienced in this field.

Basically i am too cheap and old to think about going to a good university, so I am trying to get free advice from the people who have probably completed doctorates in the relevant field. Got to be honest I say.

Anyway my contact email is at the top of the attached worksheet.

First thing that stood out to me about the distributions produced in this worksheet is how sparse the number of points is for N=17 relative to all the other values of N.

EXAMPLE_FOR_MAPLE3.mw

MAPLE_EXAMPLE_13.mw

Quantum informtion

by: Maple

Dear all , I' would like to join a group to produce quantum information tools in Maple

Different types of 'functions' -

by: Maple 7

Lesson_on_functions.mws

As the title says, a lesson on functions:  eg the -> operator, f(2), eval, evalf etc

Balance of a body with learning sequence with...

Maple 18

Using the learning sequence as an alternative to learn problems related to "balance of a body" is shown in this video; thanks to the kindness that Maple offers us in its fundamental programming syntax.

Balance_of_a_body_with_learning_sequence.mw

Lenin Araujo

Determination of the angles of the manipulator...

by: Maple 17

On the example of a manipulator with three degrees of freedom.
A mathematical model is created that takes into account degrees of freedom of the manipulator and the trajectory of the movement from the initial point to the final one (in the figure, the ends of the red curve). In the text of the program, these are the equations fi, i = 1..5.
Obviously, the straight line could be the simplest trajectory, but we will consider a slightly different variant. The solution of the system of equations is the coordinates of the points of the manipulator (x1, x2, x3) and (x4, x5, x6) in all trajectory. After that, knowing the lengths of the links and the coordinates of the points at each moment of time, any angles of the manipulator are calculated. The same selected trajectory is reproduced from these angles. The possible angles are displayed by black color.
All the work on creating a mathematical model and calculating the angles can be done without the manipulator itself, is sufficient to have only the instruction with technical characteristics.
To display some angles, the procedure created by vv is used.
MAN_2.mw

Proof of Miquel's theorem with Maple

by:

This post is devoted to the rigorous proof of Miquel's five circles theorem, which I learned about from this question. The proof is essentially very simple and takes only 15 lines of code. The figure below, in which all the labels coincide with the corresponding names in the code, illustrates the basic ideas of the code. First, we symbolically define common points of intersection of blue circles with a red unit circle  (these parameters  s1 .. s5  are the polar coordinates of these points). All other parameters of this configuration can be expressed through them. Then we find the centers  M  and  N  of two circles. Then we find the coordinates of the point  K  from the condition that  CK  is perpendicular to  MN . Then we find the point  and using the result obtained, we easily find the coordinates  of all the points  A1 .. A5. Then we find the coordinates of the point   P  as the point of intersection of the lines  A1A2  and  A3A4 . Finally, we verify that the point  P  lies on a circle with center at the point  N , which completes the proof.