Based on the information you have shared; I believe you acquired the waveform by plotting a workspace variable. Then it should contain a set of values, since computation takes place on a discrete set of values. In case it contains more than 2.5e6 values you can retrieve values for every 1 ps. But in case it is less than that, interpolate the signal such that it has minimum number of discrete values in the data and then try to sample (retrieve) the values. You can use the interpolation function, interp1 to do a 1-D data interpolation. In case you are getting it from a continuous signal source also, Matlab gets the value and stores it as a data. Try to find the variable and then try to sample for every picosecond.
If this is not what you are looking for could you, please provide a detailed explanation on how you got the waveform along with the code you have tried so that we can replicate the issue.
