I want to show r^2 and the poly1 ec on the plot

Hello, I made a poly1 ecuation with 2 column vector but I dont know how to show on the plot the R^2 value and the ecuation. I tried the text command but it's giving me an error with the () and [], help me please

h=[10;20;30;40];t1=[51.91;106.49;166.07;227.87]; t2=[51.91;54.58;59.58;61.80]; 

V=(pi*(dtr/2)^2.*h)/1000; %L
Q1=V./t1; Q2=V./t2; %L/s

f1=fit(t1,Q1,'poly1');
m1=f1.p1; b1=f1.p2; 
fit1=m1.*t1+b1;

f2=fit(t2,Q2,'poly1');
m2=f2.p1; b2=f2.p2; 
fit2=m2.*t2+b2;

subplot(2,2,1);
plot(t1,Q1,'mo',t1,fit1,'b-');
xlim([0 250]);
ylim([0.15 0.2]);
title('Caudal vs tiempos totales');
ylabel('Q (L/s)');
xlabel('t(s)');
legend('datos','ajuste',"location","best");
text(0,0.15,['R²='num2str(R_squared)])

[John D'Errico]

I split that last run-on line into separate lines, so people can read it.

[John D'Errico]

Now that I can read what you wrote, where do you define the variable R_squared?

Is that intended to be one of the R^2 coefficients from one of the two polynomial fits you did?

[Giulia Di Giorgio]

Yes, for the first plot. I didn't define it, how can I do it?

Answer 1

[Torsten]

format short g

%datos del equipo
df=6.1; %cm
hf=25; %cm
dtr=35; %cm
htr=62; %cm

%datos del usuario
V1=60; V2=0; Vr=V1-V2; %volumen de susp filtrado (L)
m1=0.1; %kg
mr=(Vr*m1)/V1; %masa real filtrada
ma=1.912; md=1.980; %pesos antes y despues de filtrar del cartucho+filtro+agua (Kg)
P=3; %psi

h=[10;20;30;40];t1=[51.91;106.49;166.07;227.87]; t2=[51.91;54.58;59.58;61.80]; %vectores altura (cm) y tiempos totales y parciales (s)

%GRAFICA Q vs t
V=(pi*(dtr/2)^2.*h)/1000; %L
Q1=V./t1; Q2=V./t2; %L/s

[f1,R]=fit(t1,Q1,'poly1');
R_squared_char = num2str(R.rsquare);
m1=f1.p1; b1=f1.p2;
fit1=m1.*t1+b1;

f2=fit(t2,Q2,'poly1');
m2=f2.p1; b2=f2.p2;
fit2=m2.*t2+b2;

subplot(2,2,1); 
plot(t1,Q1,'mo',t1,fit1,'b-');
xlim([0 250]);
ylim([0.15 0.2]);
title('Caudal vs tiempos totales'); 
ylabel('Q (L/s)');
xlabel('t(s)');
legend('datos','ajuste',"location","best");
text(10,0.155,strcat('R²= ',R_squared_char))
subplot(2,2,2); 
plot(t2,Q2,'mo',t2,fit2,'b-');
xlim([50 65]);
ylim([0.1 0.7]);
title('Caudal vs tiempos parciales'); 
ylabel('Q (L/s)');
xlabel('t(s)');
legend('datos','ajuste',"location","best");

[Giulia Di Giorgio]

Thank you very much :) it worked

Answer 2

[John D'Errico]

Read the help for fit! Look at the second argument it can return. You don't give me enough information (what is dtr, for example?) to actually run your code, so I'll just make up some data.

x = rand(10,1);
y = rand(10,1); % random data, so R^2 should be randomly near 0.
[f1,goodness]=fit(x,y,'poly1');
goodness

goodness = struct with fields:
           sse: 0.3322
       rsquare: 0.0073
           dfe: 8
    adjrsquare: -0.1168
          rmse: 0.2038

Do you see that goodness has a field named rsquare? That is the R^2 coefficient you want.

goodness.rsquare

ans = 0.0073

[Giulia Di Giorgio]

Hi John, I'll copy you the full code, I didn't do it before because it is in Spanish. I just need to be able to show de R^2 in my plot, I don't know what I'm missing. Thx

format short g

%datos del equipo
df=6.1; %cm
hf=25; %cm
dtr=35; %cm
htr=62; %cm

%datos del usuario
V1=60; V2=0; Vr=V1-V2; %volumen de susp filtrado (L)
m1=0.1; %kg
mr=(Vr*m1)/V1; %masa real filtrada
ma=1.912; md=1.980; %pesos antes y despues de filtrar del cartucho+filtro+agua (Kg)
P=3; %psi

h=[10;20;30;40];t1=[51.91;106.49;166.07;227.87]; t2=[51.91;54.58;59.58;61.80]; %vectores altura (cm) y tiempos totales y parciales (s)

%GRAFICA Q vs t
V=(pi*(dtr/2)^2.*h)/1000; %L
Q1=V./t1; Q2=V./t2; %L/s

f1=fit(t1,Q1,'poly1');
m1=f1.p1; b1=f1.p2;
fit1=m1.*t1+b1;

f2=fit(t2,Q2,'poly1');
m2=f2.p1; b2=f2.p2;
fit2=m2.*t2+b2;

subplot(2,2,1); plot(t1,Q1,'mo',t1,fit1,'b-');xlim([0 250]);ylim([0.15 0.2]);title('Caudal vs tiempos totales'); ylabel('Q (L/s)');xlabel('t(s)');legend('datos','ajuste',"location","best");text(0,0.15,['R²='num2str(R_squared)])
subplot(2,2,2); plot(t2,Q2,'mo',t2,fit2,'b-');xlim([50 65]);ylim([0.1 0.7]);title('Caudal vs tiempos parciales'); ylabel('Q (L/s)');xlabel('t(s)');legend('datos','ajuste',"location","best");

[John D'Errico]

I explained what you are missing in my answer. The variable R_squared does not just appear like magic. It will not be defined just because you want it to exist.

You need to create it. In this case, you can create it from the second return argument from fit.

[f1,goodness] = fit(t1,Q1,'poly1');
R_squared = goodness.rsquare;

Having done that, NOW you can use the value. But not until.

[Giulia Di Giorgio]

Thank you