How is math-round different from other Calc functions?

How is math-round different from other Calc functions?

[Daniele Nicolodi]

Hello,

it is possible to invoke Calc functions on quantities with units:

(calc-eval "sqrt(4.0 g)")
"2. sqrt(g)"

However, it this does not work for round():

(calc-eval "round(4.0 g)")
"round(4. g)"

Not knowing what is going on, I decided to build my own Calc function 
that does what is required:

(defmath uround (x)
   (* (round (remove-units x)) (extract-units x)))

However, this somehow does not work:

(calc-eval "uround(2.345 g)")
"uround(2.345 g)"

but it does if I replace round() with any other function:

(defmath uplus (x)
   (* (1+ (remove-units x)) (calc-eval "kg" 'raw)))

(calc-eval "uplus(2.345 g)")
"3.345 g"

Why is it so? How do I work around this?

Thank you.

Cheers,
Dan

Re: How is math-round different from other Calc functions?

[Andreas Schwab]

On Feb 01 2022, Daniele Nicolodi wrote:

> it is possible to invoke Calc functions on quantities with units:
>
> (calc-eval "sqrt(4.0 g)")
> "2. sqrt(g)"
>
> However, it this does not work for round():
>
> (calc-eval "round(4.0 g)")
> "round(4. g)"

What do you expect to happen?

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."

Re: How is math-round different from other Calc functions?

[Mattias Engdegård]

1 feb. 2022 kl. 22.12 skrev Daniele Nicolodi <daniele@grinta.net>:

> (defmath uround (x)
>  (* (round (remove-units x)) (extract-units x)))

Looks like you may need to do `math-simplify` after `remove-units`, since `math-round` only works if its argument is a value, not an unsimplified expression such as `(* (float 4 0) 1)`.

> but it does if I replace round() with any other function:
> 
> (defmath uplus (x)
>  (* (1+ (remove-units x)) (calc-eval "kg" 'raw)))

That `(1+ ...)` becomes `(math-add ... x)` and presumably `math-add` makes an effort to simplify its arguments for other reasons.

At least, this is from a cursory look at the code. Does that make sense?

Re: How is math-round different from other Calc functions?

[Daniele Nicolodi]

On 02/02/2022 09:34, Mattias Engdegård wrote:
> 1 feb. 2022 kl. 22.12 skrev Daniele Nicolodi <daniele@grinta.net>:
> 
>> (defmath uround (x)
>>   (* (round (remove-units x)) (extract-units x)))
> 
> Looks like you may need to do `math-simplify` after `remove-units`, since `math-round` only works if its argument is a value, not an unsimplified expression such as `(* (float 4 0) 1)`.
> 
>> but it does if I replace round() with any other function:
>>
>> (defmath uplus (x)
>>   (* (1+ (remove-units x)) (calc-eval "kg" 'raw)))
> 
> That `(1+ ...)` becomes `(math-add ... x)` and presumably `math-add` makes an effort to simplify its arguments for other reasons.
> 
> At least, this is from a cursory look at the code. Does that make sense?

Yes, that's it. Adding `usimplify()` I don't need to define a function 
that explicitly deals with the units:

(calc-eval "usimplify(round(2.234 g))")
"2 g"

Thank you.

Cheers,
Dan