slerp is not correct

[stla]

Hello,

I think that seq with the option slerp = TRUE is wrong. Look at this example:

> q1
          [1]
Re -0.5615167
i  -0.2325878
j   0.5615167
k  -0.5615167
> q2
          [1]
Re -0.5615167
i  -0.5615167
j   0.2325878
k  -0.5615167
> seq(q1, q2, length.out = 3, slerp = TRUE)
          [1]         [2]        [3]
Re -0.5615167 -0.57735027 -0.5615167
i  -0.2325878 -0.04417009  0.1466703
j   0.5615167  0.47071423  0.3540935
k  -0.5615167 -0.66569045 -0.7333516

The last element of the sequence is not q2. That's wrong.

The code is from * (to/from)^h. It should be from * (Ainv(from)*to)^h.

[RobinHankin]

You are absolutely correct, thanks. One difficulty is that the idiom in the package seems to work for many simple examples but

> x1 <- 1+Hi
> x2 <- 1+Hi+Hj
> seq(from=x1,to=x2,len=3,slerp=TRUE)
   [1]       [2] [3]
Re   1 1.0546907   1
i    1 1.0546907   1
j    0 0.0000000   0
k    0 0.4740726   1
> seq(from=x1,to=x2,len=3,slerp=TRUE)[3] - x2
             [1]
Re -1.110223e-16
i  -1.110223e-16
j  -1.000000e+00
k   1.000000e+00
> Mod(seq(from=x1,to=x2,len=3,slerp=TRUE)[3] - x2)
[1] 1.414214
> 

I'll patch it when I get a minute, best wishes, Robin

[RobinHankin]

Something wrong:

> x1 <- 1+Hi
> x2 <- 1+Hi+Hj
> seq(from=x1,to=x2,len=3,slerp=TRUE)
Error in is.finite(if (is.character(from)) from <- as.numeric(from) else from) : 
  default method not implemented for type 'S4'
In addition: Warning message:
In seq.default(from = x1, to = x2, len = 3, slerp = TRUE) :
 extra argument ‘slerp’ will be disregarded 
>