Mathcad 15 integrate function

@LucMeekes 
I try to use your method to calculate the value.

but Mathcad can't calculate it.

Hi,

You need to send the data file for the pulse:- EPC2045.txt

We can then use your data.

Cheers

Terry

Hi Jason,

Just to answer all your questions:

Do you have any document about spline and interp function can provide to me?

cs=cspline(vx,vy).

vx is a column vector of the x values, vy is the column vector of the y values,

the cubic spline solution sets up a cubic function y=a.x^3 + b.x^2 +c.x + d for each interval between adjacent points.

it then solves for all the a,b,c,d values using the following constraints at the ends of each interval:

each cubic must pass through the end points.

the first derivative of adjacent cubics are equal at the meeting point

the second derivative of adjacent cubics are equal at the meeting point to give smooth curves either side off a point

the first and last equation can be cubic cspline(), a polynomial in second degree pspline() or simple linear equation lspline()

what is returned as cs is all the a,b,c,d's in a long column vector.

y=linterp(cs,vx,vy,x) allows you to use all the stored a,b,c & d in cs and choose the correct set.

it the uses the appropriate a,b,c &d equation for the x value entered and finds the value of y=a.x^3 + b.x^2 +c.x + d

Because I don't very understand what's the function of the spline and why you need to interpret the spline.

As above cs is just a list of a,b,c,d values. You need to use the interp function to determine which a,b,c,d to use for y=a.x^3 + b.x^2 +c.x + d at the point desired.

if I don't interpret the spline I can't do the integrate?

Werner and Luc have shown you can do it without using splines.

Above explanation explains why you need to use linter(cs,vx,vy,x) to get a y value at the right x for integration of a spline.

In this example cspline does a good job with no oscillations and the resulting integrations are close in value with whatever method you use.

Cheers

Terry