Spline Toolbox | ![]() ![]() |
Syntax
Description
fnplt(f)
plots the function, described by f
, on its basic interval.
If is univariate, the following is plotted:
If is bivariate, the following is plotted:
surf
).
surf
).
If is a function of more than two variables, then the bivariate function, obtained by choosing the midpoint of the basic interval in each of the variables other than the first two, is plotted.
fnplt(f,arg1,arg2,arg3,arg4)
permits you to modify the plotting by the specification of additional input arguments. You can place these arguments in whatever order you like, chosen from the following list:
'-.'
or '*'
; the default is '-'
.
1
.
'j'
to indicate that any jump in the univariate function being plotted should actually appear as a jump. The default is to fill in any jump by a (near-)vertical line.
[a,b]
, to indicate the interval over which to plot the univariate
function in f
. If the function in f is arg
, the command fnplt(f,arg,...)
has the same effect as the command fnplt(fnbrk(f,arg),...)
. The default is the basic interval of f
.
points = fnplt(f,...)
plots nothing, but the two-dimensional points or three-dimensional points it would have plotted are returned instead.
Algorithm
The univariate function described by
f
is evaluated at 101 equally spaced sites x
filling out the plotting interval. If is real-valued, the points
are plotted. If
is vector-valued, then the first two or three components of
are plotted.
The bivariate function described by
f
is evaluated on a 51-by-51 uniform grid if is scalar-valued or
-vector-valued with
and the result plotted by
surf
. In the contrary case, is evaluated along the meshlines of a 11-by-11 grid, and the resulting planar curves are plotted.
See Also
Cautionary Note
The basic interval for in B-form is the interval containing all the knots. This means that, e.g.,
is sure to vanish at the endpoints of the basic interval unless the first and the last knot are both of full multiplicity
, with
the order of the spline
. Failure to have such full multiplicity is particularly annoying when
is a spline curve, since the plot of that curve as produced by
fnplt
is then bound to start and finish at the origin, regardless of what the curve might otherwise do.
Further, since B-splines are zero outside their support, any function in B-form is zero outside the basic interval of its form. This is very much in contrast to a function in ppform whose values outside the basic interval of the form are given by the extension of its leftmost, respectively rightmost, polynomial piece.
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