MATLAB: Simple question about scatter/data plots

data plotsscatter plots

Say I have two scripts. The first one is called RideData. It contains four arrays that are called speed, distance, climb, and calories. Those are the four variables assigned to four arrays. The second script is the main one where I want to create a scatter/data plot. If I wanted to use the speed and distance arrays from the first script to plot in the second script, how would I call the first script in order to plot using those arrays?

Best Answer

Your best option is to change your RideData script into a function (see documentation about functions) and have that function return those arrays, something like that:

function [speed, distance, climb, calories] = RideData()
   % enter your functionality here
end

then you simply call the function from your main script like that:

[speed, distance, climb, calories] = RideData();
% now you can plot your stuff

Related Solutions

MATLAB: How Do I Perform a Surface of Revolution of a 2D Plot that is not a Function

The function "cylinder" can generate a surface based on a profile by rotating that profile around the x-axis and then aligning the resulting surface with the z- axis:

https://www.mathworks.com/help/matlab/ref/cylinder.html

However, the cylinder function treats the profile that is being passed into it as having monotonically increasing x-values; i.e. that the profile is a function. Thus, when you are trying to rotate a curve that is like a sideways parabola (which is not a function) it will not produce the desired result.

In order to visualize this surface, as well as get the X,Y,and Z coordinates of what the resulting surface would be, you need to parameterize the function in terms of two new variables, "t" and a "theta". This allows you to define an "R(t,x)" that one can use to generate the desired Y and Z values for the resulting surface of revolution.

In this example, you define a "t" to go between 0 and 4. This is because in this curve, the x-values go from -1 to 1 and back to -1. This accounts for a total "distance" traveled of 4. You then define your "x" values in terms of "t". R(t,x) in this case will be "acos(x) + 4" for "t" values less than 2 and will be "-acos(x) + 4" for values of "t" greater than 2.

Once you have your x(t) and R(t,x) defined all that is left is to define the Y and Z coordinates of the surface revolution. This is done by defining a new variable "theta" that goes in between 0 and 2*pi. At every x value, there is a corresponding R(t,x) value that represents the curve at that point in 2D space. When we rotate that around in 3D space, we have Y and Z values that are defined as follows (given to us by basic trigonometry):

Y = R(t,x) * cos(theta)

Z = R(t,x) * sin(theta).

Thus, you have a way to get your X,Y, and Z coordinates. From there, you can use the "surf" function to visualize the surface, or simply use the them for other sorts of processing.

Please see the attached script for more details.

MATLAB: How to add line of best fit to plot

You are not accepting the coefficients from polyfit() - they basically are thrown away. Even if you did do

coefficients = polyfit(climb, calories, 2);

you still need to compute the fitted values, like

numFitPoints = 1000; % Enough to make the plot look continuous.
xFit = linspace(min(climb), max(climb), numFitPoints);
yFit = polyval(coefficients, xFit);
hold on;
plot(xFit, yFit, 'r-', 'LineWidth', 2);
grid on;

See attached demo, which produces the plot below.

Best Answer

Related Solutions

MATLAB: How Do I Perform a Surface of Revolution of a 2D Plot that is not a Function

MATLAB: How to add line of best fit to plot

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