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9 years, 13 days
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Inconsistent behavior of eval in piecewi...

vv 13040 Maple
eval piecewise
March 19 2018
0 5

Strange (inconsistent) behavior of eval in piecewise

 

> 

restart;#####################
> 

a:=2:
> 

p:=piecewise(x<a, 1/(x-a), x=a, 22, 33);

p := piecewise(x < 2, 1/(-2+x), x = 2, 22, 33)

 (1)
> 

eval(p, x=a);

22

 (2)
> 

restart;#####################
> 

a:=Pi:
> 

p:=piecewise(x<a, 1/(x-a), x=a, 22, 33);

p := piecewise(x < Pi, 1/(-Pi+x), x = Pi, 22, 33)

 (3)
> 

eval(p, x=a);

Error, (in eval/piecewise) numeric exception: division by zero

  
> 

restart;#####################
> 

a:=Pi+ln(2):
> 

p:=piecewise(x<a, 1/(x-a), x=a, 22, 33);

p := piecewise(x < Pi+ln(2), 1/(-Pi-ln(2)+x), x = Pi+ln(2), 22, 33)

 (4)
> 

eval(p, x=a);

22

 (5)
> 

restart;#####################
> 

a:=Pi+1:
> 

p:=piecewise(x<a, 1/(x-a), x=a, 22, 33);

p := piecewise(x < Pi+1, 1/(-Pi-1+x), x = Pi+1, 22, 33)

 (6)
> 

eval(p, x=a);

Error, (in eval/piecewise) numeric exception: division by zero

  
> 

restart;#####################
> 

a:=gamma:
> 

p:=piecewise(x<a, 1/(x-a), x=a, 22, 33);

p := piecewise(x < gamma, 1/(-gamma+x), x = gamma, 22, 33)

 (7)
> 

eval(p, x=a);

Error, (in eval/piecewise) numeric exception: division by zero

  
> 

#######################
> 

f:=x->piecewise(x<Pi, 1/(x-Pi), x=Pi, 22, 33);

f := proc (x) options operator, arrow; piecewise(x < Pi, 1/(x-Pi), x = Pi, 22, 33) end proc

 (8)
> 

f(Pi);

22

 (9)
> 

 


Download piecewise-strange.mw

Difficult to explain?...

vv 13040 Maple
digits evalb
February 11 2018
1 7

Some of these seem to be difficult to explain ...

 

> 

restart;
> 

Digits:=3;

3

 (1)
> 

u:=1.23456;

1.23456

 (2)
> 

A := [1.23456, 1.23456+0, 1.23456+x+0, 1.23456+(x+0)];
B := [u,       u+0,       u+x+0,       u+(x+0)];

[1.23456, 1.23, 1.23+x, 1.23456+x]

  

[1.23456, 1.23456, 1.23456+x, 1.23456+x]

 (3)
> 

lprint(A); lprint(B);

[1.23456, 1.23, 1.23+x, 1.23456+x]

[1.23456, 1.23456, 1.23456+x, 1.23456+x]

  
> 

is(A[1]=A[2]),    is(A[3]=A[4]);

true, true

 (4)
> 

evalb(A[1]=A[2]), evalb(A[3]=A[4]);

true, false

 (5)
> 

is(A=B);
is~(A=~B);

false

  

[true, true, true, true]

 (6)
> 

evalb(A=B);
evalb~(A=~B);

false

  

[true, true, false, true]

 (7)
> 

 

Download Difficult-to-explain.mw

Maple should try harder...

vv 13040 Maple
complex max rootof
February 08 2018
2 11
> 

restart;
> 

f:=5*x^3-5*x+1;

5*x^3-5*x+1

 (1)
> 

s:=[solve(f)]; evalf(%);  # All the roots are real

[(1/30)*(-2700+(300*I)*219^(1/2))^(1/3)+10/(-2700+(300*I)*219^(1/2))^(1/3), -(1/60)*(-2700+(300*I)*219^(1/2))^(1/3)-5/(-2700+(300*I)*219^(1/2))^(1/3)+((1/2)*I)*3^(1/2)*((1/30)*(-2700+(300*I)*219^(1/2))^(1/3)-10/(-2700+(300*I)*219^(1/2))^(1/3)), -(1/60)*(-2700+(300*I)*219^(1/2))^(1/3)-5/(-2700+(300*I)*219^(1/2))^(1/3)-((1/2)*I)*3^(1/2)*((1/30)*(-2700+(300*I)*219^(1/2))^(1/3)-10/(-2700+(300*I)*219^(1/2))^(1/3))]

  

[.8788850663-0.2e-9*I, -1.088033915-0.2598076212e-9*I, .2091488484+0.2598076212e-9*I]

 (2)
> 

max(s);  # ?

Error, (in simpl/max) complex argument to max/min: (1/30)*(-2700+(300*I)*219^(1/2))^(1/3)+10/(-2700+(300*I)*219^(1/2))^(1/3)

  
> 

type(s,list(realcons)); # Wrong, the type realcons should not be purely syntactic; or is it?

false

 (3)
> 

R:=convert(s,RootOf):
> 

max(R);  #  For nested RootOfs fails

Error, (in simpl/max) complex argument to max/min: (1/30)*RootOf(_Z^3+2700-300*RootOf(_Z^2+1, index = 1)*RootOf(_Z^2-73, index = 1)*RootOf(_Z^2-3, index = 1), index = 1)+10/RootOf(_Z^3+2700-300*RootOf(_Z^2+1, index = 1)*RootOf(_Z^2-73, index = 1)*RootOf(_Z^2-3, index = 1), index = 1)

  
> 

sort(s): evalf(%);  # Wrong

[.8788850663-0.2e-9*I, .2091488484+0.2598076212e-9*I, -1.088033915-0.2598076212e-9*I]

 (4)

 

Workaround

 

> 

S:=[seq(RootOf(f,x,index=i),i=1..3)];

[RootOf(5*_Z^3-5*_Z+1, index = 1), RootOf(5*_Z^3-5*_Z+1, index = 2), RootOf(5*_Z^3-5*_Z+1, index = 3)]

 (5)
> 

evalf(S);

[.2091488484, .8788850662, -1.088033915]

 (6)
> 

min(S);max(S);  # OK

RootOf(5*_Z^3-5*_Z+1, index = 3)

  

RootOf(5*_Z^3-5*_Z+1, index = 2)

 (7)
> 

sort(S);   # Wrong!

[RootOf(5*_Z^3-5*_Z+1, index = 1), RootOf(5*_Z^3-5*_Z+1, index = 2), RootOf(5*_Z^3-5*_Z+1, index = 3)]

 (8)
> 

################################
> 

r:=(sqrt(2)+I)^3 + (sqrt(2)-I)^3;

(2^(1/2)+I)^3+(2^(1/2)-I)^3

 (9)
> 

type(r,realcons);  # Purely syntactic?

false

 (10)
> 

type(expand(r),realcons);

true

 (11)
> 

max(r,13);  # Even for such a simple expression?

Error, (in simpl/max) complex argument to max/min: (2^(1/2)+I)^3+(2^(1/2)-I)^3

  
> 

 


Download TryHarder.mw

Strange output for Vector...

vv 13040 Maple 2017
vector print
December 11 2017
0 4

Here are two inocent Vectors.

> 

V1 := Vector[row]([`+`, 1, 2]);

_rtable[18446744074366295326]

 (1)
> 

V2 := Vector[row]([1, `+`, 2]);

_rtable[18446744074366288110]

 (2)
> 

lprint(V1);

Vector[row](3, {1 = `+`, 2 = 1, 3 = 2}, datatype = anything, storage = rectangular, order = Fortran_order, shape = [])

  

 

The questions:

 

1.  Try to guess the Maple's answer for:

 

> 

V1, V2;

 

2. Try to explain.

 


Download v1v2.mw

A simple evalf/Int crashes Maple...

vv 13040 Maple 2017
evalf int crash
December 06 2017
0 8 
evalf(Int(x*(1-2*x^(3/10))^(10./3),x=0..1));  # Crashes Maple

Note that:

int(x*(1-2*x^(3/10))^(10./3),x=0..1);
int(x*(1-2*x^(3/10))^(10/3),x=0..1);
are OK.

(Windows 7, Maple 2017.3, 64 bit)

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