semilogy

Create a vector of x-coordinates and a vector of y-coordinates. Create a log-linear plot of x and y, and call the grid function to show the grid lines.

x = 1:100;
y = x.^2;
semilogy(x,y)
grid on

Create a vector of x-coordinates and two vectors of y-coordinates. Plot two lines by passing comma-separated x-y pairs to semilogy.

x = 1:100;
y1 = x.^2;
y2 = x.^3;
semilogy(x,y1,x,y2)
grid on

Define vector x as the installments on a 20 year loan. Define vector y as the cumulative cost of a $1000 loan with an interest rate of 8%. Plot the cumulative cost at each installment.

P = 1000; 
npayments = 240;  
rate = 0.08/12; 
mpayment = P*(rate*(1+rate)^npayments)/(((1+rate)^npayments) - 1);
x = 1:240;
y = x * mpayment;
semilogy(x,y);
grid on

Change the y-axis tick values and tick labels by calling the yticks and yticklabels functions. Then create x- and y-axis labels by calling the xlabel and ylabel functions.

yticks([10 50 100 500 1000])
yticklabels({'$10','$50','$100','$500','$1000'})
xlabel ('Installment')
ylabel('Cumulate Cost')

Create a set of x- and y-coordinates and plot them in a log-linear plot. Specify the line style as 'o' to display circular markers without connecting lines. Specify the marker fill color as the RGB triplet [0 0.447 0.741], which corresponds to a dark shade of blue.

x = linspace(1,1000,15);
y = (1./x) * 10000;
semilogy(x,y,'o','MarkerFaceColor',[0 0.447 0.741])
grid on

Create two sets of x- and y-coordinates and display them in a log-linear plot. Specify a dashed line for the first set of coordinates. Then display a legend in the upper left corner of the plot by calling the legend function and specifying the location as 'northwest'.

x = 1:100;
y1 = x.^2;
y2 = x.^3;
semilogy(x,y1,'--',x,y2)
legend('x^2','x^3','Location','northwest')

When you specify only one coordinate vector, semilogy plots those coordinates against the values 1:length(y). For example, define y as a vector of 5 values. Create a log-linear plot of y.

y = [0.1 0.2 1 10 1000];
semilogy(y)
grid on

If you specify y as a matrix, the columns of y are plotted against the values 1:size(y,1). For example, define y as a 5-by-3 matrix and pass it to the semilogy function. The resulting plot contains 3 lines, each of which has x-coordinates that range from 1 to 5.

y = [ 0.1    1     10
      0.2    2     20
      1.0    10    100
      10     100   1000
      1000   10000 100000];

semilogy(y)
grid on

Since R2022a

A convenient way to plot data from a table is to pass the table to the semilogy function and specify the variables to plot.

Create a table containing two variables. Then display the first three rows of the table.

Input = (1:100)';
Output = Input.^2;
tbl = table(Input,Output);
head(tbl,3)

    Input    Output
    _____    ______

      1        1   
      2        4   
      3        9   

Plot the Input variable on the x-axis and the Output variable on the y-axis. Return the Line object as p, and turn the axes grid on. Notice that the axis labels match the variable names.

p = semilogy(tbl,"Input","Output");
grid on

To modify aspects of the line, set the LineStyle, Color, and Marker properties on the Line object. For example, change the line to a red dotted line with point markers.

p.LineStyle = ":";
p.Color = "red";
p.Marker = ".";

Since R2022a

Create a table containing three variables. Then display the first three rows in the table.

Input = (1:100)';
Output1 = Input.^2;
Output2 = Input.^3;
tbl = table(Input,Output1,Output2);
head(tbl,3)

    Input    Output1    Output2
    _____    _______    _______

      1         1          1   
      2         4          8   
      3         9         27   

Plot the Input variable on the x-axis and the Output1 and Output2 variables on the y-axis. Add a legend. Notice that the legend labels match the variable names.

semilogy(tbl,"Input",["Output1","Output2"])
grid on
legend

Create a tiled chart layout in the 'flow' tile arrangement, so that the axes fill the available space in the layout. Next, call the nexttile function to create an axes object and return it as ax1. Then display a log-linear plot by passing ax1 to the semilogy function.

tiledlayout('flow')
ax1 = nexttile;
x = 1:100;
y1 = x.^2;
semilogy(ax1,x,y1)

Repeat the process to create a second log-linear plot.

ax2 = nexttile;
y2 = 1./x;
semilogy(ax2,x,y2)

Create a log-linear plot containing two lines, and return the line objects in the variable slg.

x = 1:100;
y1 = x.^2;
y2 = x.^3;
slg = semilogy(x,y1,x,y2);

Change the width of the first line to 3, and change the color of the second line to purple.

slg(1).LineWidth = 3;
slg(2).Color = [0.4 0 1];

Insert NaN values wherever there are discontinuities in your data. The semilogy function displays gaps at those locations.

Create a pair of x- and y-coordinate vectors. Replace the twentieth y-coordinate with a NaN value. Then create a log-linear plot of x and y.

x = 1:50;
y = x.^2;
y(20) = NaN;
semilogy(x,y)