Error when trying to plot a polynomial with data.

I have written a code to determine the equation of a line from some data. I need the slope and y-intercept which I have found without a problem but I would also like to plot the polynomial over the data but it keeps giving me an error regarding the vestor sizes not matching.

This is my code

t = [10; 20; 30; 40; 50; 60] ; %time in units of min

Ca = [2.45; 1.74; 1.23; 0.88; 0.62; 0.44] ; %concentration of bromine in ppm

%Need to determine the change in time and concentration over the course of

%the study

dCa = [Ca(2) - Ca(1); Ca(3) - Ca(2); Ca(4) - Ca(3); Ca(5) - Ca(4);...

Ca(6) - Ca(5)] ;

dt = [t(2) - t(1); t(3) - t(2); t(4) - t(3); t(5) - t(4); t(6) - t(5)] ;

%Need to divide the change in concentration by the change in time then take

%the natural logarith of -dCa/dt to find the y coordinates for our plot

diff = dCa./dt ;

y = log(-diff) ;

%Now take the natural logarith of the concentration to determine the x

%values for our plot

x = log(Ca) ;

%Now we can plot the data but since we need to hte same number of data

%points we will only use data points 2-6 for ln(Ca)

plot(x(2:6),y,'bd')

xlabel('ln(Ca)') ;

ylabel('ln(-dCa.dt)') ;

hold on ;

%Use polyfit to determine the equation of the line that best fits our data

%but need to use the same number of data points so we will only use the 2-6

%elements of the ln(Ca)

p = polyfit(x(2:6),y,1) ;

%Print the results of the polynomial

fprintf(['The genrated equation for the line has a slope of m = %4.4f ' ...

'and a y-intercept of b = %4.4f\n'],p(1),p(2)) ;

%Now that we have the equation of the line we will plot it over the data

%points

plot(p,x(2:6),y) ;

legend('Location','NorthWest') ;

And this is the error it keeps giving me

Error using plot

Vectors must be the same length.

Error in HW5 (line 48)

plot(p,x(2:6),y) ;

Answer 1

[Star Strider]

Use the polyval function.

[Mikolaj Malinski]

Do you mean to use it with my already generated p equation in the following way:

y1 = polyval(p,x)

plot(x,y1,'r-')

or did you have a differnet method in mind

[Star Strider]

The first option.

I don’t know of any other ways to use it.

[Mikolaj Malinski]

I used it as you suggested and it worked. Thank You

[Star Strider]

As always, my pleasure!