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How to plot a linear function?

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Jenni on 7 Feb 2024
Commented: William Rose on 9 Feb 2024
Here is my function and I am trying to plot a linear function in form:
y = b_0 + b_1x.
How could I plot this function using the result values b_0 and b_1?
Here is my function code called "sovittaja":
function [b, bci] = sovittaja(x,y,delta_y)
%%Helper variables:
s_1 = sum(1./(delta_y.^2));
s_2 = sum((x.*y)./(delta_y.^2));
s_3 = sum(x./(delta_y.^2));
s_4 = sum(y./(delta_y.^2));
s_5 = sum(x.^2./(delta_y.^2));
%%Defining D:
D = (s_1*s_5)-(s_3)^2;
%%Analyyttiset lausekkeet:
b_1 = (1/D)*((s_1)*(s_2)-(s_3)*(s_4));
b_0 = (1/D)*((s_5)*(s_4)-(s_3)*(s_2));
%%Margin of errors:
delta_b_1 = sqrt((1/D)*(s_1));
delta_b_0 = sqrt((1/D)*(s_5));
%%Indexs of matrix bci :
bci_11 = b_0 - delta_b_0;
bci_12 = b_1 - delta_b_1;
bci_21 = b_0 + delta_b_0;
bci_22 = b_1 + delta_b_1;
%% Return values:
b = [b_0, b_1];
bci = [bci_11,bci_12;bci_21,bci_22];
And here is what I want to do with the function "sovittaja":
clear all
close all
% Measurement:
% Frequency:
% Voltage:
% Margin of Error:
So, how could I plot my result to a linear function y = b_0 + b_1x?
And additional question: How could I do the same thing by using command fitlm?
Thank you for the help!
John D'Errico
John D'Errico on 7 Feb 2024
Edited: John D'Errico on 7 Feb 2024
Why would you want to use fitlm to plot a line? It is not a tool that creates plots. So what are you asking? I think you want to know a tool that can fit a line through your points, using some given weights at those points. I am not entirely sure if the "margin of error" is a set of weights, or it is a set of hard constraints that the line is not allow to pass.
Plotting a line is easy enough, even trivial. Choose two points on the line. Plot them, connecting them with a line.
William Rose
William Rose on 7 Feb 2024
The fitlm help at is very nice. Read it, try the examples, and you will be good.

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Accepted Answer

William Rose
William Rose on 7 Feb 2024
Edited: William Rose on 8 Feb 2024
[edit: Fix typo: change "values at" to "values are"]
It looks like you want to plot measured data as well as the best-fit straight line.
The measured values are x and y. The predicted values are x and b(0)+b(1)*x.
Please see the instructions and examples here
It also seems like you might want error bars on your plot. If so, see the description and the examples here:
Jenni on 8 Feb 2024
Excellent, thank you for the helpful advice and the links!

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