MATLAB: alternative to CSAPE function?

In summary, MATLAB offers an alternative to the CSAPE function with its own spline interpolation method. This method, called the "spline" function, allows for the creation of a smoother curve and offers more control over the shape of the curve compared to the CSAPE function. Additionally, the spline function is better suited for handling data with non-uniform spacing. However, the CSAPE function may still be preferred for certain applications, such as when working with a large number of data points.
  • #1
PhysMaster
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MATLAB: alternative to CSAPE function? (Aerospace application)

Hi,
I need it to spline fit an airfoil. This function is special because it has "end conditions". So the trailing edge will remain intact. I am looking for an alternative because I don't have Spline Toolbox and this is the only function I need.

MathWorks Original Function Link: http://www.mathworks.com/access/helpdesk/help/toolbox/splines/index.html?/access/helpdesk/help/toolbox/splines/csape.html&http://www.mathworks.com/cgi-bin/texis/webinator/search/?db=MSS&prox=page&rorder=750&rprox=750&rdfreq=500&rwfreq=500&rlead=250&sufs=0&order=r&is_summary_on=1&ResultCount=10&query=csape&submitButtonName=Search"

I found this: http://www.mathworks.com/matlabcentral/fileexchange/17610 but it doesn't say anything about end conditions.

Please let me know of any other (maybe user created) function that can do this. Just a tool, it can be for excel anything else.

Thank you.
 
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  • #2
I believe no one would waste time creating another function that has been already created. I don't know about other softwares, but surely excel doesn't have something like that.

To the reader: if you have come looking for an alternative, like the OP, I'll advise you to buy the Toolbox. Matlab doesn't publish it's source code for functions, so there is almost no way you can find an exact duplicate function.

Currently, the spline fitting functions are in the Curve Fitting Toolbox:
https://in.mathworks.com/help/curvefit/spline-fitting.html
 
  • #3
PhysMaster said:
MATLAB: alternative to CSAPE function? (Aerospace application)

Hi,
I need it to spline fit an airfoil. This function is special because it has "end conditions". So the trailing edge will remain intact. I am looking for an alternative because I don't have Spline Toolbox and this is the only function I need.

What sort of end conditions? Specifying the first derivatives at the endpoints is a fairly standard constraint, I think called "clamped cubic splines".

it shouldn't be that hard to homebrew your own spline routine, as ultimately it comes down to a linear system. Read a little literature on how to set up the equations, define your linear system, and use Matlab's built-in solver. (HELP SLASH).

Implementation note: In writing my own spline routines, I've always found it convenient to work in normalized variables that go from 0 to 1 on each segment (that makes the equations incredibly simple), or relative coordinates that go from 0 to delta-x on each segment (almost as simple). This also tends to keep the coefficients small and the expressions numerically stable.
 

FAQ: MATLAB: alternative to CSAPE function?

1. What is the CSAPE function in MATLAB and what is its purpose?

The CSAPE function in MATLAB stands for "Cubic Spline Approximation in Piecewise Polynomial Form." It is used to generate a cubic spline interpolation of a given set of data points. The purpose of this function is to create a smooth curve that passes through all the data points, making it easier to analyze and visualize the data.

2. What is an alternative to the CSAPE function in MATLAB?

An alternative to the CSAPE function in MATLAB is the Spline Toolbox, which also provides tools for creating spline interpolations and curve fitting. It offers more flexibility and advanced options for manipulating the spline curve, such as controlling the smoothness and boundary conditions.

3. Are there any limitations of using the CSAPE function in MATLAB?

Yes, there are some limitations to using the CSAPE function in MATLAB. It can only handle 1-dimensional data and cannot handle data with repeated points. It also requires the data to be in ascending order, and if there are any missing values, it will interpolate them based on the available data points.

4. Can I customize the spline curve created by the CSAPE function in MATLAB?

Yes, you can customize the spline curve created by the CSAPE function in MATLAB. You can control the smoothness of the curve by adjusting the number of pieces and the smoothing parameter. You can also specify different types of boundary conditions, such as natural, periodic, or clamped, to control how the curve behaves at the endpoints.

5. How accurate is the spline interpolation created by the CSAPE function in MATLAB?

The accuracy of the spline interpolation created by the CSAPE function in MATLAB depends on the smoothness of the data and the number of pieces used to construct the curve. Generally, it provides a good approximation of the data, but it may not capture all the details or small fluctuations in the data. It is always recommended to visually inspect the interpolation to ensure its accuracy.

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