Simple Math with Variables

romeograham

I am trying to use a Feature Studio to set up project variables - to be used in a single Document.

I have, say, two specifications (Hmax & Hmin). I can set up Variables (setVariable) no problem. 

setVariable(context, "Hmax", 30 * millimeter);
setVariable(context, "Hmin", 28 * millimeter);
setVariable(context, "Hrange" = (Hmax - Hmin)); /*how do I do math in this variable?*/

Now, I'd like to make a new "Hrange" Variable, that does a little simple math with those two variables:

setVariable(context, "Hrange" = (Hmax - Hmin)); /*how do I do math in this variable?*/

However, this expression doesn't work. I tried a few different ways to do it, but even this simple thing is beyond my understanding. I'm not sure what search terms will help in the Documentation - haven't had luck with the searches that made sense to me.

Any help would be great!
Thanks
Romeo

_anton

The setVariable calls store a variable value in the context. You can use getVariable to retrieve the values. E.g.,

const Hmax = getVariable(context, "Hmax");
const Hmin = getVariable(context, "Hmin");
setVariable(context, "Hrange", Hmax - Hmin);

romeograham

Ah - so I need to tell FS that my previously-declared Variable is a Constant (const) that can be used in downstream calculations...something like that?

Thanks for the quick help @_anton !

_anton

So the getVariable call just returns the value (or throws, if it's not defined - see here). You could also write

setVariable(context, "Hrange", getVariable(context, "Hmax") - getVariable(context, "Hmin"));

romeograham

I think I like that better - I can keep the entire definition of the setVariable "Hrange" on one line. 

NeilCooke

Or just define them all as variables at the top of the code, then you can do all the calculations you like before calling setVariable at the end. More code, but easier to read. 

romeograham

@NeilCooke
I thought that's how I started out, but wasn't successful. 
Can you paste a little example here?

ilya_baran

I would actually do them in a map, something like:

var v = {};
v.Hmax = 30 * millimeter;
v.Hmin = 28 * millimeter;
v.Hrange = v.Hmax - v.Hmin;
...
for (var entry in v)
    setVariable(context, entry.key, entry.value);

NeilCooke

ilya_baran said:

I would actually do them in a map, something like:

var v = {};
v.Hmax = 30 * millimeter;
v.Hmin = 28 * millimeter;
v.Hrange = v.Hmax - v.Hmin;
...
for (var entry in v)
    setVariable(context, entry.key, entry.value);

That's what I was going to put (honestly) 

NeilCooke

And save yourself some typing by putting at the top

const mm = millimeter;

romeograham

Thanks @NeilCooke and @ilya_baran - that mapping seems to be a tidy way to do it.

EvanReese

Seems like I've been doing this the wordy way. Thanks, @ilya_baran for the for loop solution instead.