Bold font in math mode

[hasky67]

Hi,
I am strugling with writting bold font in math mode. Please, do I miss something? In text mode it works fine.
$$ \eqalign{\dot{p} &= {\bf v} \cr \dot{v} &= R(a_m-a_b) + g} \eqmark $$

But during compilation, it gives me
! Undefined control sequence. <argument> \_bsansvariables \_sansgreek \_bsansdigits \_inmath #1->\_relax \_ifmmode #1 \_fi <argument> \dot {p} &= {\bf v} \cr \dot {v} &= R(a_m-a_b) + g \eqalign ...}$\_hskip .5\_eqspace \_hfil \_crcr #1 \_crcr }}\_thinsk l.44 \dot{v} &= R(a_m-a_b) + g} \eqmark $$ ?
Any help please?

Thanks

[olsak]

The problem is not reproducible. Your line

$$ \eqalign{\dot{p} &= {\bf v} \cr \dot{v} &= R(a_m-a_b) + g} \eqmark $$

is OK. It does not generate any error. Give full example.
The error message is not fully copied. The most important thing: where the lines in the error message end, is missing. So, we cannot guess what control sequence is undefined.

[olsak]

The \_sansgreek was renamed to \_bsansgreek in commit b7dc0e9#diff-4c7648fdf8b4da4cca53d5103a0f13490bfcf5f1b50d78a23a9c2af48f4ec9f5 Maybe, you are using macros which were valid before this commit.