742 Reputation

13 Badges

1 years, 0 days

MaplePrimes Activity

These are replies submitted by sursumCorda

@Carl Love Many thanks. Since convert(..., 'elsymfun') currently does not support arbitrary polynomials, I try to use PolynomialReduce to convert a non-symmetric polynomial into a sum and a remainder (with fixed variable ordering) (and then reconstruct the original polynomial from them). But it appears that this time none of orders works: 

P := (a - c*1)*(b - a*2)*(c - b*4):
B := [(a + b + c)**3, (a*b + b*c + c*a)*(a + b + c), a*b*c]:
PolynomialReduce(P, B, [a, b, c]);
Error, (in quo) arguments must be polynomial in c
PolynomialReduce(P, B, [a, c, b]);
Error, (in quo) arguments must be polynomial in b
PolynomialReduce(P, B, [b, a, c]);
Error, (in quo) arguments must be polynomial in c
PolynomialReduce(P, B, [b, c, a]);
Error, (in quo) arguments must be polynomial in a
PolynomialReduce(P, B, [c, a, b]);
Error, (in quo) arguments must be polynomial in b
PolynomialReduce(P, B, [c, b, a]);
Error, (in quo) arguments must be polynomial in a

@Carl Love Thanks. Another strange thing is that sometimes the output seems incorrect: 

PolynomialReduce(x^5 - x*y^6 - x*y, [x^2 + y, x^2 - y^3], [x, y]):
expand(inner([x^2 + y, x^2 - y^3], %[1]) + %[2]);
             6    3  3    5      4    3        2      
         -x y  + x  y  + x  + x y  - x  y - x y  - x y

PolynomialReduce(x^5 - x*y^6 - x*y, [x^2 + y, x^2 - y^3], [y, x]):
expand(inner([x^2 + y, x^2 - y^3], %[1]) + %[2]);
            13    7  3    9      6    3  3    5      
           x   + x  y  - x  - x y  - x  y  + x  - x y

Though the result is often not completely unique, yet I think that at least the reconstructed polynomial should equal the original one. Perhaps there exists some bug? 

@Carl Love Thanks. But I find a strange thing:

[PolynomialReduce](2*x^4 + y^3 - x^2 + y^2, [x^3 - x, y^3 - y], [x, y]);
                    [           2    2    ]
                    [[2 x, 1], x  + y  + y]

[PolynomialReduce](2*x^4 + y^3 - x^2 + y^2, [x^3 - x, y^3 - y], [y, x]);
Error, (in quo/polynom) division by zero

@Carl Love Thanks. The only regret is that this does not output the other term "[x + y, 2*(y - a)]" (although Maple may have found it in the internal).

Besides, I think that the origional function is also an extension of solve(identity(…, ...), ...) and PDEtools:-Solve(…, ..., 'independentof' = ...) when working with polynomials, since those coefficients in the second example can be easily obtained by them when a=0. But if the remainder is not zero, these two commands will not work.

@Rouben Rostamian  Six years have passed; regretfully, such convenient syntax is still not built into Maple. What is the reason?

@sand15 Thanks. Strangely, the older Eigenvals function will return the newer default LinearAlgebra:-Eigenvectors form (instead of the linalg:-eigenvectors form).

@Preben Alsholm I read it in 

showstat(`evalf/matrixexp`, 66);

`evalf/matrixexp` := proc(A)
local a, t, ss, s, i, i1, bk, p, z, n, m, j, k, l, M, N, oldD, islist, tmp;
  66   if _EnvLinalg95 = true and islist then
       end if
end proc

I believe that it is similar to: 

  1. MTM:-expm
  2. `linalg/matrixexp`
  3. linalg:-matrixexp
  4. linalg:-exponential
  5. Student:-LinearAlgebra:-MatrixExponential, and 
  6. LinearAlgebra:-MatrixExponential.

@Preben Alsholm Thanks. The problem is: If I understand right, in theory, shouldn'd setting “_EnvLinalg95 := true:” only impact on the obsolete `linalg` package (without influencing the most recent `LinearAlgebra` package)? 

The modern `LinearAlgebra` package was originally introduced in Maple 6, which was released in 2000. Twenty-three years have passed; while `LinearAlgebra:-Eigenvalues` and `LinearAlgebra:-EigenConditionNumbers` work well, the relevant `LinearAlgebra:-Eigenvectors` still has a cryptic dependency upon `_EnvLinalg95` (even if I do not “with(linalg):”). This is really weird.

I am not very familiar with signal processing, but the spline option in the new SignalProcessing:-SavitzkyGolayFilter command seems to be explained in SignalProcessing:-DifferentiateData's documentation: 

• … the savitzkygolay method … use extrapolation on the left and right ends to lengthen data container X so that the derivative of order n is of the same size as X. This extrapolation can be performed in three ways:
    • extrapolation=periodic: The data is assumed to be periodic, so that Xi + m = Xi for each integer i with m being the size of X.
    • extrapolation=polynomial: Using the CurveFitting['PolynomialInterpolation'] command, interpolating polynomials of degree (at most) d are used to extend X on the left and right.
    • extrapolation=spline: Using the CurveFitting['ArrayInterpolation'] command, splines of degree (at most) d are used to extend X on the left and right.

(The Wikipedia article says that this method "has been extended for the treatment of 2- and 3-dimensional data". Can Maple's SignalProcessing['SavitzkyGolayFilter'] be generalized?)

@awass Even if ordinary users read the help page, they can be still confused.
For instance, the documentation of `convert/Vector` mentions: 

• copy : truefalse
Indicates whether a new rtable should be allocated when converting from other rtable types such as Array or Matrix. The default is false, meaning that convert will attempt to provide a reference to the existing rtable instead of allocating a new one.


Sv := <1, 2>:
Tv := convert(Sv, Vector, copy = false):
evalb(Sv = Tv);

Will this not confuse users? I think it will.

@nm Sorry, there is a typo; I have edited my reply. Thanks. 


@nm Thanks. There are also other less nice things in Maple. While I believe that somebody has noticed them before, I cannot find such questions/posts in this forum. For example,

subs[eval](x = 1, '1 - x'):
(subs[eval](x = 1, '1 - x')):
1 - subs[eval](x = 1, 'x'):
1 - (subs[eval](x = 1, 'x')):
use x = 1 in 1 - x end:

 are all allowed, but strangely, 

(use x = 1 in 1 - x end):
1 - use x = 1 in x end:
1 - (use x = 1 in x end):

 is invalid. This is just a trivial example, yet it is still typical. If I wish to do so, I shall have to use 

1 - if true then use x = 1 in x end fi:


1 - (to 1 do use x = 1 in x end od):

which is quite awkward.

@vv Thanks. In this example, although I can use "output=..." for LinearAlgebra:-Eigenvectors, this is not valid for MTM:-eig. 

The major problem is: if someone sends me an encrypted procedure that uses built-in keyword `_nresults` but do not provide any output option, when I only request the second output and he/she rejects modifying the source code, shall I have to assign a worthless variable (and then clear it) instead of simply ignoring it at the beginnibg in the syntax level?

@nm I change some options such that the plot looks more attractive, yet I also do not know how to translate Mma's StreamPoints (that is, closeness of streamlines) back into Maple. 

Here is the same thing in Mathematica

According to How to | Plot a Vector Field, Mma's StreamPlot is not identical to Maple's DEtools:-phaseportrait/DEtools:-DEplot; the equivalent seems to be VectorPlot

Unfortunately, I do not know how to explicitly draw streamlines (in other words, flow paths, instead of field vectors) in Maple.

@ider I do not know how to fix it. (Though you can use a until-loop, this will be somewhat clumsy.) But the reason is written in the documentation: 

The environment variable Order … does not necessarily represent the order of the error term ….
1 2 3 4 5 6 7 Last Page 1 of 16