# Trouble with mrmath

Hi Folks
I am struggling mrmath and the struggle is so basic I am worried I am doing something very stupid. But I simply can not see what.

So I try to use mrmath and the usage is simple enough, but I can’t seem to be able to do the simple most things with it, but always get the error
mrmath: [ERROR] unexpected value supplied for argument “operation” (valid choices are: mean, median, sum, product, rms, norm, var, std, min, max, absmax, magmax)
I use the command:

mrmath b0s.mif mean mean_b0_AP.mif –axis 3

I think this might be related to the use of a long dash (–) instead of a regular dash (-) in the `–axis` option. This means the command doesn’t recognise `–axis` as an option, but treats it as a regular argument. When that happens, the command sees what it thinks are 5 regular arguments, and therefore assumes arguments 1, 2 & 3 are input images, argument 4 (`–axis`) is the operation to be performed, and the last argument (the number `5`) is the output image…

Try using a regular dash rather than a long one. I think these issues tend to happen when commands are copy-pasted from documents that were written using MS Word, since it tends to ‘autocorrect’ dashes into long dashes quite routinely, it’s actually quite difficult to get it to stop…

Yes, yes, that did it.
Awesome. Thanks.
M.