Using the Flexible Spline function (FlexSpline) in Excel

This video demonstrates how to use the Flexible Spline (FlexSpline) function of 'Data Curve Fit Creator Add-in' in Excel. The Flex spline is a spline fit to your data, but it allows you to specify the slope of the curve that you want at any data point.

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http://www.srs1software.com/DataCurve...

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Closed Caption:

in this video I'm going to show you the
flex spline function in data curved
creator adding flex spline function is a
spline function that gives you a little
bit more control over how your final
spline curve looks and it does this by
allowing you to specify the slope of the
spline curve at one or more data points
and you'll see how all that works so in
order to show you how that works
I've got some sample data here I've got
some x and y-values the X values go from
a range of 0 to 30 and it's
corresponding Y values go from about 2
to about eight now let's say that I
wanted to put a spline curve through
those points i set up a column of values
here to calculate the spline values for
this data now my sample data that I'm
going to use it starts at minus-5 and it
goes to 35 so it starts before my sample
data and it goes until it you know to
after my sample data and first off let
me try just a standard cubic spline not
sure what kind of results i get with
that so I'm gonna go and say equals and
then at the start function button now of
course I've got data curved creator
adding installed here so under my user
defined functions here i have a bunch of
these data perfect creator functions and
the first one here to explain let me
select that
so first let me select the x and y
values of the source data so these are
the X values here now first thing I'm
going to do is I'm going to hit after i
select those values I'm gonna hit f4 and
you notice when I just did that dollar
signs appear in my range dollar signs
make that those cell references absolute
references and I want that because I'm
gonna be copying this formula to a bunch
of different cells and i always want to
be referring back to the same source
data
so now let's choose my y-values select
that range here and f4 and now my new x
value which is the first value for which
shall be evaluating this cubic spline
for that's my first value value there in
the column i'll say okay now I've
already wired up this plot to show the
values here as a red line and you'll see
it when i copy the values down so I copy
down and see it looks like a standard to
explain now looks pretty good by
definition of cubic spline of course
always goes through all data points in
your dataset but you notice that
let's say if we look at the at the
beginning and end of our spline function
you notice that at the ends the spline
curve continues to move up and at the at
the beginning it continues to move down
so if we're extrapolating out a lot it
would be going to continue to miss the
curve would continue to move up now
let's say that we didn't want that
let's say that we wanted our curve to
just flattened out and stay flat forever
before and after the datasets well how
would we do that well that's a typical
you know a good example of where the
Flex blind would come in handy so let me
go now and remove the cubic spline
points and let me go and use the flex
line so again i'll hit equal sign insert
function this time i'll go i'll select
the Flex spline say okay same thing
select my x-values select my y-values
select my new X . this is the first
point in our sample data there and this
new argument here slope at each point
this is where you can specify the slope
at each data point and so for that i'm
going to select this column this bunch
of cells right next to my data and hit
f4 going to make that an absolute
reference i'll say okay and before I put
any slopes in i'm going to copy the
values down and you can see that we get
pretty similar results as we had before
now i'm going to go and just label this
column now and as I mentioned for one or
more of the points you can put in slope
value so as i said i want the curve to
be flat at the beginning and at the end
and to go on flat forever so what I'll
do is for my first data point i'll put a
slope of zero hit enter and you notice
that this slope suddenly flattened out
and from my last data point of putting a
slope of 0 and you know it's going to
hit enter this is going to flatten out
and it does so this is just a way to
give you a lot more flexibility a lot
more control over your final over your
final spline curve you can try it out
download data curve fit creator add-in
from www.sresre.com that