Hcfyk

I am new to LaTeX. I know how to write basic equations in LaTeX. However, the following equation seems to be too difficult for me. Please help me with this. Thank you.

I'd not use the inner brace, but a standard notation for the minimum, just split across lines.

documentclass{article}

usepackage{amsmath}



DeclareMathOperator{lev}{lev}



begin{document}



begin{equation*}

lev_{a,b}(i,j)=

  begin{cases}

  max(i,j) & text{if $min(i,j)=0$,} \[1ex]

  begin{aligned}[b]

  minbigl(lev_{a,b}&(i-1,j)+1, \

            lev_{a,b}&(i,j-1)+1, \

            lev_{a,b}&(i-1,j-1)+1_{(a_ine b_j)}

      bigr)

  end{aligned} & text{otherwise.}

end{cases}

end{equation*}



end{document}

You might prefer the following realization, which is obtained by using begin{aligned} instead of begin{aligned}[b].

amsmath's cases is defined for this. The horizontal space between the bracket and the inside contents is very good.

documentclass{article}

usepackage{amsmath}

begin{document}

[

mathrm{lev}_{a,b}(i,j)=begin{cases}

    max(i,j)&text{if $min(i,j)=0$,}\

    minbegin{cases}

        mathrm{lev}_{a,b}(i-1,j)+1\

        mathrm{lev}_{a,b}(i,j-1)+1\

        mathrm{lev}_{a,b}(i-1,j-1)+1_{(a_ine b_j)}

    end{cases} &text{otherwise.}

end{cases}

]

end{document}

It seems to me that you are writing a document which uses lev() function quite often. In this case, you should define a new macro to avoid repetition (I use DeclareMathOperator, which is the best way for this, thanks to egreg's suggestion in his comment).

documentclass{article}

usepackage{amsmath}

%newcommand{lev}{mathrm{lev}}: not good

DeclareMathOperator{lev}{lev}

begin{document}

[

lev_{a,b}(i,j)=begin{cases}

    max(i,j)&text{if $min(i,j)=0$,}\

    minbegin{cases}

        lev_{a,b}(i-1,j)+1\

        lev_{a,b}(i,j-1)+1\

        lev_{a,b}(i-1,j-1)+1_{(a_ine b_j)}

    end{cases} &text{otherwise.}

end{cases}

]

end{document}

If you use the function lev a lot then it is a good idea to define it as follows

newcommand{lev}[2]{mathrm{lev}_{a, thinspace b} (#1, thinspace #2)}

Just type lev and you will get the function with two arguments to enter.

documentclass{article}

usepackage{amsmath}

usepackage{booktabs}

usepackage{array}



begin{document}



newcommand{lev}[2]{mathrm{lev}_{a, thinspace b} (#1, thinspace #2)}    

begin{equation}

lev{i}{j} = leftlbrace

    begin{array}{l l}

        max(i, thinspace j) & text{if~} min(i, thinspace j) =0,

    \

        min leftlbrace hspace{-1mm}

                begin{array}{l}

                    lev{i-1}{j} + 1

                \

                addlinespace[0.5mm]

                    lev{i}{j-1} + 1

                \

                addlinespace[0.5mm]

                    lev{i-1}{j-1} + 1_{(a_{i} neq b_{j})}

                end{array}



            right. & text{otherwise}.

    end{array}

            right.

end{equation}



end{document}