semilogy(Y) //    It generates a plot using a base 10 logarithmic scales for the y-axis and linear scales for the x-axis. It plots the column of Y versus their index.
semilogy(X1,Y1,...)//         It plots all Yn versus Xn pairs.
semilogy(X1,Y1,LineSpec,...)// It plots all the lines described by the Xn,Yn,LineSpec triples. LineSpec determine line style, marker symbol, and color of the plotted lines.
semilogy(...,'PropertyName',PropertyValue,...)//  It sets property values for all the charting lines created by semilogy. 
semilogy(ax,...)//     It generates the line in the axes specified by ax instead of in the current axes (gca). The option ax precedes any of the input argument combinations in the previous syntaxes.
h = semilogy(...)//   It returns a vector of chart line objects.

x=t,y=e^t,0≤t≤2π
t=linspace (0, 2*pi,200);
semilogy(t, exp(t))
grid