Xrhrft

I wonder how to solve my problem.
In 'normal' matrix we have a square brackets but I need to write a brackets like in photo

Could you help me?

I'm using usepackage{amsmath}.

I guess you're looking for leftlceil and rightrfloor.

documentclass{article}

usepackage{amsmath} % for 'matrix' environment

begin{document}

[

leftlceil

begin{matrix}

a_1 & a_2 & dots & a_n \

b_1 & b_2 & dots & b_n 

end{matrix}

rightrfloor

]

end{document}

It makes sense to define new environments for this task:

documentclass{article}

usepackage{amsmath}



makeatletter

newcommand{newmatrix}[3]{% #1 = prefix, #2/#3 = left/right delimiters

  newenvironment{#1matrix}{left#2env@matrix}{endmatrixright#3}%

}

makeatother



newmatrix{cf}{lceil}{rfloor}

newmatrix{fc}{lfloor}{rceil}



begin{document}



[

begin{cfmatrix}

a_1 & a_2 & dots & a_n \

b_1 & b_2 & dots & b_n

end{cfmatrix}

ne

begin{fcmatrix}

a_1 & a_2 & dots & a_n \

b_1 & b_2 & dots & b_n

end{fcmatrix}

]



end{document}

The “prefix” can be any string not already in use.

With a bit more work it can support defining the *-variant in the mathtools style, that is, accepting an optional argument to set the column alignment, and the “small” variant all in one swoop.

documentclass{article}

usepackage{amsmath,mathtools}



MHInternalSyntaxOn

makeatletter

newcommand{newmatrix}[3]{%

  % #1 = prefix, #2/#3 = left/right delimiters

  newenvironment{#1matrix}

    {left#2env@matrix}

    {endmatrixright#3}%

  newenvironment{#1matrix*}[1][c]

    {left#2MT_matrix_begin:N ##1}

    {MT_matrix_end:right#3}

  MT_fenced_sm_generator:nnn{#1smallmatrix}{#2}{#3}

}

makeatother

MHInternalSyntaxOff



newmatrix{cf}{lceil}{rfloor}



newmatrix{fc}{lfloor}{rceil}



begin{document}



begin{gather*}

begin{cfmatrix}

a_1 & a_2 & dots & a_n \

b_1 & b_2 & dots & b_n 

end{cfmatrix}

ne

begin{fcmatrix}

a_1 & a_2 & dots & a_n \

b_1 & b_2 & dots & b_n 

end{fcmatrix}

\

begin{cfmatrix}

a_1 & a_2 & dots & a_n \

b_1 & b_2 & dots & b_n 

end{cfmatrix}

ne

begin{fcmatrix*}[r]

111 & 44 & dots & -2 \

2 & 333 & dots & 5 

end{fcmatrix*}

\

begin{cfsmallmatrix}

a_1 & a_2 & dots & a_n \

b_1 & b_2 & dots & b_n 

end{cfsmallmatrix}

ne

begin{fcsmallmatrix}

a_1 & a_2 & dots & a_n \

b_1 & b_2 & dots & b_n 

end{fcsmallmatrix}

end{gather*}



end{document}