## 792 Reputation

9 years, 240 days

## What does abs(F) mean in package Physic...

Maple 2020

I am a newbie in the use of the Physics package.
As I'm interested in modeling dynamic articulated systems, I began reading the example about Mechanics (Statics).

My question is quite simple: let F some vector force of components a * _i and b * _j , what does abs(F) represent?

I naively thought that abs(F)  was the modulus of F and expected it to be non negative. But I get some negative values (as in the tutorial example for some values of angle alpha.

## Maximum length of file names...

Maple 2020

I inadvertently discovered that the save command (and probably read, write, export and import commands too?) returns an error (something like "can't write ...") when the file length is too large (265 in my case).

Is this documented somewhere?
Is there a way to exceed this limit?
Assuming D=".../" and F="xxx.m", can we set the path of the directory D to some value and then use save something, F instead of save something cat(D, F) ?

## How to run programmatically Windows Powe...

Maple 2020

I use Maple 2020 on a Windows 10 PC.

The command ssystem("CMD") enables to launch any Windows command accessible from the shell.
But how to launch a PowerShell command?

For instance ssystem("get-process") returns -1 (not surprising in fact for get-process is not a shell process).
How can I tell Maple that this command is to be found in the PowerShell ?

And even, I this possible for, in the ssystem help page, it's said that not all the command can be launched by ssystem

TIA

## Maple doesn't seem to compute correctly ...

Maple 2020

I have just come across this curious but really boring problem.
In the code snippet below, expr1 and expr2 are identical.

```restart:
data := [a=1, b=2]:
convert(
piecewise(And(x(t) > a, x(t) < b), 1, 0),
Heaviside
):
expr1 := eval(eval(%, data),  x(t)=z):
plot(expr1, z=0..3);

convert(
piecewise(And(z > a, z< b), 1, 0),
Heaviside
):
expr2 := eval(%, data),:
plot(expr2, z=0..3);```

But if I change the parameterization of the problem, expr2 is still correct but expr1 is not

```restart:
data := [d=1.5, a=0.5]:
convert(
piecewise(And(x(t) > d-a, x(t) < d+a), 1, 0),
Heaviside
):
expr1 := eval(eval(%, data),  x(t)=z):
plot(expr1, z=0..3);

convert(
piecewise(And(z > d-a, z< d+a), 1, 0),
Heaviside
):
expr2 := eval(%, data),:
plot(expr2, z=0..3);
```

Where does this come from?

## Could you explain me why this doesn't w...

Maple
```restart:

alias(f=f(t)):
alias(g=g(t)):

diff([f, g], t):  #ok

a := [alias()]:
diff(a, t);
[0, 0]```

More generally, how can we differentiate a list of aliases without naming them explicitely?