how to get matlab to differentiate in increments of 1 rather than 0.01

Hi there. I am trying to use forward velocity data from a motorcycle to find the suspension position. When doing this i need the acceleration so i differentiate the data i have using diff() to give the acceleration. When i do this however the answer is a factor of 100 out. When trying to find the cause i noticed that the recording module takes readings every 100th of a second. i get that MATLAB is essentially finding the gradient between my two data points then the next, then the next. My question is, how do i get matlab to find dx/dt in one second increments rather than 100th's of a second? thanks

[José-Luis]

I don't get it.

If you are doing this numerically, a finer gradient would just be a linear interpolation. Am I missing something?

Just resample() your data and calculate the gradient on that.

[Robert U]

Hi Ross Hanna,

either you take every 100th sample which would result in a loss of information or you have to remember that dx/dt in time discrete systems is approximated by (x(t2)-x(t1))/(t2-t1) where diff(x) is giving you only the x-part of the approximate.

In order to correct the faulty factor 100 you would have to divide diff(x) by the corresponding time steps.

Kind regards,

Robert