DefTotrans

1. summary Convert text expressions into coordinate transformation functions
2. labels Reference,Version1

_(This page applies only to the 1.x branch of SVGFig.)_

totrans

Coordinate transformation functions are Python callables that map a pair of arguments to a pair of output values. This can be cumbersome, so totrans converts a minimal text expression to such a function.

This is applied automatically by [ClassFig Fig], [ClassPlot Plot], [ClassFrame Frame], and all plottable objects.

Arguments

• totrans(expr, vars, globals, locals)*

	expr		_*required*_		text expression of the form "f(x,y), g(x,y)" or a Python callable
	vars		_default_=("x", "y")		argument names; if only one value is given, the expression is treated as a complex function
	globals		_default_=None		dict of global variables used in the expression; you may want to use Python's builtin `globals()`
	locals		_default_=None		dict of local variables

All symbols from Python's [http://docs.python.org/lib/module-math.html math library] are in scope, so you can say things like `cos(0.1)*x - sin(0.1)*y, sin(0.1)*x + cos(0.1)*y`.

If vars has only one element (e.g. ["z"]), the expression will be treated as a complex function, using symbols from Python's [http://docs.python.org/lib/module-cmath.html cmath library] instead.

If expr is already a Python callable, it will be converted from complex to a function of two real variables.

Examples

Simply swap two variables:

totrans("y, x")

Example use of globals.

totrans("c*x - s*y, s*x + c*y", globals={"c": math.cos(0.1), "s": math.sin(0.1)})

If "c" and "s" are variables defined in Python's global scope, the same can be accomplished with

totrans("c*x - s*y, s*x + c*y", globals=globals())

These yield the same transformation: }}} totrans("z2", vars=("z",)) totrans(lambda z: z2) }}}