When I run this patch + subpatch:


(fexpr~ in a 1 sample vector.pd ) I get this message in the PD parent window:

expr: input vector index <  -VectorSize, (vector x1[-1.000000])
$x1
-
1 


fexpr~: index assumed to be = -1
fexpr~: no error report till next reset

Is that an error message? If so, what is fexpr~ complaining about? The patch seems to work fine. [rpole~] (which also looks back one sample) works too but doesn't generate any messages.

@jameslo there are some hints in the helpfile. fexpr~ can not look back one sample if the blocksize/vectorsize is only one sample. To look back one sample it needs a block size of at least two samples.
By the way, there is no reason to use block~ with fexpr~ (except if you want to look back more then 64 samples).

@whale-av No, the math I wrote is the math I meant. It's just an expression to access the previous sample.

@solipp Yes, this example is functionally pointless because I've removed everything that wasn't necessary to generate that message. In the original I'm reading from and writing to a 1 sample table to reduce an audio feedback delay to 1 sample.

RE help:

so I think I've met the requirement. Plus it seems to work, though admittedly my test is weak. And when I think about it, if fexpr~ allows access to the previous sample, then even with a 64 sample vector it would have to access the last sample of the previous vector while processing the first sample of the current vector. It's the same as when the vector size is 1. So I read the restriction on the index values to mean "Sorry, I'm not gonna buffer an arbitrarily large number of past vectors for you. Be happy with the one I'm giving you."

@jameslo true. Or more like "You got me! i have this little extra sample for you. Please don't ask again!"