Skip to main content
R
remslie14-Alexandrite
14-Alexandrite
October 20, 2020
Solved

Velocity function will not integrate

  • October 20, 2020
  • 2 replies
  • 3123 views

Hi,

I am trying to simulate a base excitation using a velocity versus time waveform as the base excitation. I have imported an excel file and developed a velocity time function using "linterp". When I try to integrate this it flags an error.

Further down the sheet I use an indefinite integral to derive the base input displacement from my velocity waveform. Is this OK. Any assistance would be appreciated. Cheers Ross

Best answer by AlanStevens

1. In M15 the indefinite integral of sin(x) works ok!

g0.jpg

 

2.  I've fixed some errors in the sheet and pointed out some mistakes in units - see attached.

2 replies

L
LucMeekes23-Emerald IV
23-Emerald IV
October 20, 2020

Your GY(t) is defined for only numerical applications. Asking for the indefinite integral (the integral without borders) is a symbolic operation. You can't even numerically evaluate an indefinite integral for symbolically known functions like sin(x):

LucMeekes_0-1603175719966.png

in contrast to:

LucMeekes_1-1603175748962.png

To determine the integral of the dataset that you input, simply summing is the best way.

Your datapoints are discrete values. You cannot achieve more accuracy by interpolation.

So:

LucMeekes_2-1603176536625.png

Success!

Luc

 

R
remslie14-AlexandriteAuthor
14-Alexandrite
October 21, 2020

Luc,

Many thanks for your interest, knowledge  and feedback on my integration issue.

Cheers

Ross

A
AlanStevens19-TanzaniteAnswer
19-Tanzanite
October 20, 2020

1. In M15 the indefinite integral of sin(x) works ok!

g0.jpg

 

2.  I've fixed some errors in the sheet and pointed out some mistakes in units - see attached.

L
LucMeekes23-Emerald IV
23-Emerald IV
October 20, 2020

"In M15 the indefinite integral of sin(x) works ok!"

Yes, symbolically, but try that numerically...

 

Luc

A
AlanStevens19-Tanzanite
19-Tanzanite
October 20, 2020

@ Luc

"Yes, symbolically, but try that numerically..."

 

Of course not numerically!  As you demonstrated, the result is a function, not a number (though I missed the fact that you'd shown a numerical = rather than a symbolic -> !).

Terms & ConditionsCookie settingsAccessibility statement