semilogx(Y)  //  It generates a plot using a base 10 logarithmic scale for the x-axis and a linear scale for the y-axis. It plots the column of Y versus their index. The values in Y can be numerical, datetime, duration, or categorical values.
semilogx(X1,Y1,...) //  It plots all Yn versus Xn pairs. 
semilogx(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.
semilogx(...,'PropertyName',PropertyValue,...)// It sets property values for all charting lines created by semilogx.
semilogx(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 combination in the previous syntax.
h = semilogx(...)//   It return a vector of chart line objects.

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