Graph builder issues (again!)

I am trying to build a graph to test an equation i have found for calculating LAI against the Biophysical processor.
In the first screenshot the editor accepts the formula (which is actually 0.57exp(2.33NDVI), but the editor won’t allow me to enter the ‘E’ constant)

But when I try and add the link to ‘BandMerge’, throws the error seen in the second screenshot.

please can someone explain why this happens?
I have also added the .xml file for the graph (i think it has saved it properly, but it doesn’t usually!)
myGraph_gndvi_gci_EVI_EVI2_write_imageafter_subset.xml (5.8 KB)

Oh, and just for fun, when i go back into the expression editor, it has lost the ndvi source!:

Hello Matt,

Actually, the expression 0.57 * exp(2.033 * ndvi) should work.
Alternatively, you can use 0.57 * pow(E, 2.033 * ndvi)

The ^ does not mean ‘to the power’ but is a bitwise XOR operator.

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The Help button should open “Band Maths Expression Editor”, which includes a list of the available operators.

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You are absolutely right, we need to take this on-board in the near future.

This is already on board

Thanks @marpet,
for some reason the expression now seems to be working!
I guess its just the vagaries of the graph builder!