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Rouben Rostamian

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18 years, 274 days
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These are questions asked by Rouben Rostamian

Misbehaving plot in Maple 2023...

Rouben Rostamian 8259 Maple 2023
plot
February 25 2024
1 1
> 

restart;

Here we have a pretty well-behaved trig function:

> 

y := t -> 144*cos(t)^6 - 216*cos(t)^4 + 32*cos(t)^3 + 81*cos(t)^2 - 24*cos(t) + 17;

proc (t) options operator, arrow; 144*cos(t)^6-216*cos(t)^4+32*cos(t)^3+81*cos(t)^2-24*cos(t)+17 end proc

> 

plot(y(t), t=0..2*Pi, view=0..35);

Maple 2023 plots y^(3/2) with a strange artifact at t = Pi:

> 

plot(y(t)^(3/2), t=0..2*Pi, view=0..200);

Any reason for that?  Maple 2021 and earlier used to produce the correct plot:

  

Download bug-in-plot.mw

Looks like a regression bug in dsolve...

Rouben Rostamian 8259 Maple 2023
ode dsolve differential-equations
February 20 2024
0 0

Applying Maple 2023's dsolve to the ODE shown below yields the solution y(t)=0 which is obviously incorrect.  Maple 2021 and earlier used to give a nonzero (albeit not very useful) answer.

> 

restart;
> 

F := (t-1)*(t-2)/(t^2+1)^3*(Heaviside(t-2)-Heaviside(t-1));

(t-1)*(t-2)*(Heaviside(t-2)-Heaviside(t-1))/(t^2+1)^3

> 

plot(F, t=0..4);

> 

de := diff(y(t),t,t) + diff(y(t),t) = F;

diff(diff(y(t), t), t)+diff(y(t), t) = (t-1)*(t-2)*(Heaviside(t-2)-Heaviside(t-1))/(t^2+1)^3

> 

ic := y(0)=0, D(y)(0)=0;

y(0) = 0, (D(y))(0) = 0

Huh?

> 

dsolve({de,ic}, y(t));

y(t) = 0

Specifying method=laplace will make that work, but how is an

unsuspecting user to know that what's obtained above is incorrect?

Download dsolve-bug.mw

How to plot this function?...

Rouben Rostamian 8259 Maple 2023
plot
December 08 2023
1 1

The attached worksheet shows that Maple 2023 produces an incomplete plot of a function.  Maple 2021, however, produces the full graph.  I wonder if Maple 2023's behavior is due to a bad setting in my environment or a plotting bug in Maple.

> 

restart;
> 

kernelopts(version);

`Maple 2023.2, X86 64 LINUX, Oct 25 2023, Build ID 1753458`

> 

y := -cos(sqrt(x))*x^3/(-x^2 + 24*cos(sqrt(x)) + 12*x - 24);

-cos(x^(1/2))*x^3/(-x^2+24*cos(x^(1/2))+12*x-24)

> 

plot(y, x=0..1);

Here is the graph of the same function plotted correctly in Maple 2021:

Download cannot-plot.mw

Bug in simplify piecewise...

Rouben Rostamian 8259 Maple 2023
simplify piecewise physics
October 20 2023
0 2

This used to work in Maple 2022.  Something is broken in 2023. 

 

> 

restart;
> 

kernelopts(version);

`Maple 2023.1, X86 64 LINUX, Jul 07 2023, Build ID 1723669`

> 

Physics:-Version();

`The "Physics Updates" version in the MapleCloud is 1561 and is the same as the version installed in this computer, created 2023, October 20, 22:58 hours Pacific Time.`

> 

U := Int(exp(-1/4*t - 1/4*x)*piecewise(x < -2, 1, x < -1, -x - 1, 0), x = -t .. 0);

Int(exp(-(1/4)*t-(1/4)*x)*piecewise(x < -2, 1, x < -1, -x-1, 0), x = -t .. 0)

> 

Uval := simplify(value(U));

Uval := `simplify/piecewise/unfactor`(4*piecewise(t < 1, 0, t < 2, t-5+4*exp(`&ndash;`((1/4)*t)+1/4), 2 <= t, 1+4*exp(`&ndash;`((1/4)*t)+1/4)-4*exp(`&ndash;`((1/4)*t)+1/2)))

> 

eval(Uval, {x=5, t=6});

`simplify/piecewise/unfactor`(4+16*exp(-5/4)-16*exp(-1))

> 

 
 

Download simplify-piecewise-bug.mw

 

Inverse Laplace transform on Maple 2023 ...

Rouben Rostamian 8259 Maple 2023
inverse laplace
October 19 2023
1 9

Maple thinks the inverse Laplace transform of 1/(s+a) is exp(a*t).  It should be exp(−a*t).

This used to work correctly in Maple 2022.  Something got messed up in 2023.

> 

restart;
> 

kernelopts(version);

`Maple 2023.1, X86 64 LINUX, Jul 07 2023, Build ID 1723669`

> 

with(inttrans):
> 

exp(-a*t);

exp(-a*t)

> 

laplace(%, t, s);

1/(s+a)

> 

invlaplace(%, s, t);

exp(a*t)

 

Download laplace-transform-bug.mw

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