Thanks, Nils!
The following question probably belongs to sage-support, but it is
directly related:
It does not seem to make a difference whether I do
sage: var('T_a')
or
sage: T_a = var('T_a')
but William's example does not work if I do
sage: var2('T_a', 'Air temperature (K)')
instead of
sage: T_a = var2('T_a', 'Air temperature (K)')
??
Cheers
Stan
On 20/09/11 17:47, Nils Bruin wrote:
On Sep 20, 12:36 am, Stan Schymanski<schym...@gmail.com> wrote:
Since this is done in the units package already, is there a way to
formally save the units of e.g. T_a as units.temperature.Kelvin and then
have something like:
sage: T_a = 300
sage: T_a
300 Kelvin
You can of course write T_a=300*units.temperature.kelvin and
essentially get this, see the doc.
Otherwise: python semantics get in the way. What you propose would
require T_a to be statically typed to be a temperature, but that is
not how python works. The instruction "T_a=300" rebinds the identifier
T_a to the object 300 (which, thanks to sage's preparser, really is
Integer(300)). Once you execute a new assignment, T_a is bound to a
fresh object and all type info hangs off that object, not T_a.
T_a=300*units.temperature.kelvin
T_a=10*units.length.meter
If you want a separate type that denotes temperatures in kelvin, you
could define the appropriate (sub)class and get something like:
sage: T_a=temperature_in_kelvin(300) #just special printing
sage: T_a
300 Kelvin
or
sage: T_a=temperature_in_kelvin(300) #construct unit expression
sage: T_a
300*kelvin
but that probably has virtually no benefits for you above what you can
already do by just multiplying with the right unit.
[Thank you, William, for pointing out that units already subclass
symbolic expressions to set docs]
[apologies the empty reply before]
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