my plot is blank?

my graph is generated but there are no lines that appear on the graph

clear;
close all;
clc;
%load the cross section distance along river
rivercrossection = load('Cross_Sections_DistanceAlongRiver_X_Y.txt', '\t');
% load the pre-dredging cross sections
pre_dredging_crossection = load("PreDredgingCS.txt");
pre_dredging_crossection = reshape(pre_dredging_crossection, [], 1);
%load post-dredging cross section
post_dredging_crossection = load("PostDredgingCS.txt");
post_dredging_crossection = reshape(post_dredging_crossection, [], 1);
% Calculate the volume of sediment using the detailed cross section
volume_crossection = sum(post_dredging_crossection - pre_dredging_crossection) * (rivercrossection(2) - rivercrossection(1)) * (pre_dredging_crossection(2) - pre_dredging_crossection(1));
% Calculate the velocities pre dredging
velocitiesB1 = (200 / (rivercrossection(2) - rivercrossection(1))) * (pre_dredging_crossection(2) - pre_dredging_crossection(1)) / (pre_dredging_crossection);
%calculate the velocities post dredging
velocitiesB2 = (200 / (rivercrossection(2) - rivercrossection(1))) * (post_dredging_crossection(2) - post_dredging_crossection(1)) / (post_dredging_crossection);
% Plot the current velocities for the cross section
figure(2);
plot(velocitiesB1,velocitiesB2,'b-');
xlabel("transect");
ylabel("Current velocity (m/s)");
title("Current velocities before and after dredging");

Answer 1

[Cris LaPierre]

There are 3 things to check right away

1. that your variable velocitiesB1 and velocitiesB2 are not empty
2. that those variables have at least 2 values
3. that those values are not NaN

If you are plotting a single point, you won't be able to see it because your plot style does not include a marker style. Add one to see if this is the case.

plot(velocitiesB1,velocitiesB2,'b-*');

Answer 2

[Image Analyst]

What does this show in the command window?

whos velocitiesB1
whos velocitiesB2
plot(velocitiesB1,velocitiesB2,'b-*');

Please see: Debugging in MATLAB | Doug's MATLAB Video Tutorials