And, as one more note on this topic, a comment about 3dDWItoDT:

The b-matrix, which is essentially what is used in the tensor calculations, is given by:
b = b g g^T,
where b is the DW magnitude (what we call b-value, a scalar) and g is the DW gradient (a 3-component vector, which usually has unit-magnitude); the operation of the gradients here is an outer product, producing the 3x3 b-matrix.

If one were going to estimate b just from a single input gradient, then one would have to have the b-value information included in that gradient using an appropriate scale. From the equation above, the most appropriate scale would be the square root of the b-value, so that one could define the new input quantity as h = sqrt(b) g, with the result that:
b = h h^T = [sqrt(b) g] [sqrt(b) g]^T = sqrt(b)*sqrt(b) g g^T = b g g^T.

All this is fine and well, and if one entered something like h into 3dDWItoDT, everything would be fine. *However*, most programs don't output gradient values scaled by the square root of the b-value, they output a gradient scaled by the full b-value: that is, they make some k = b g. This would create a problem in the above equation, where the calculated b-matrix would be:
b' = k k^T = b² g g^T,
which would be wrong (except in the special case that the b-value was 1). If a gradient scaled as in k is input, then the *correct* b-matrix would be:
b = (k k^T) / |k| = (b² g g^T) / b = b g g^T.

Therefore, instead of changing the input format of the gradients to be scaled by a square root of the b-value, 3dDWItoDT will assume that the gradient is scaled by the full b-value, and adjust internally to produce the correct b-matrix (using the last equation). 3dDWUncert will also assume this, and so will 1dDW_Grad_o_Mat for making its b-weighted inputs/outputs.