how do I fit a double exponential equation? there are two double exponential waveforms and I need to fit the equation into each waveform

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Siti Fatimah Mohamed Hisham 2019-4-20

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评论： Walter Roberson 2019-4-20

This is how the waveforms look like. I transferred the datas from Excel. The data was obtained using an oscilloscope when I compared the lightning voltage waveforms for with and without an attenuator. Now my job is to fit the double exponential equation into each of these waveforms to compare the difference for the two situations (with and without attenuator).

The double exponential equation for lightining voltage is:

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Walter Roberson 2019-4-20

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You can use cftool with a custom equation.

Be warned that sum of exponential are notoriously difficult to fit. If your initial values are not quite close to the best values then it is quite common for the fitting coefficients to be very different from the best coefficients.

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Siti Fatimah Mohamed Hisham 2019-4-20

oh. how should/do I put the bounds so to obtain better fitting?

Walter Roberson 2019-4-20

Click on Fit Options to enter upper and lower bounds. You will not be able to directly code to ensure that d>b. However you can rewrite d as b+doffset and set the lower bound on doffset to 0.

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