How can I get the X value of the red stars on my graph after interpolation? And could I have the values be put on the graph?

x=[4.75,2,.85,.389,.15,.075,0];
y=[92.09,40.61,17.2,4.78,1.29,.72,0];

plot(x,y);
grid on;

semilogx(x,y);
xlabel('Particle Size (mm)');
ylabel('Percent Passing (%)');

y60=60;
xi=interp1(y,x,y60);
hold on
semilogy(xi,y60,'*r');

y30=30;
xi=interp1(y,x,y30);
hold on
semilogy(xi,y30,'*r');

y10=10;
xi=interp1(y,x,y10);
hold on
semilogy(xi,y10,'*r');

[Walter Roberson]

? The x values associated with the red stars are the three xi vectors that you calculate: just make sure you do not overwrite them as you proceed.

Answer 1

[KSSV]

x=[4.75,2,.85,.389,.15,.075,0]; 
y=[92.09,40.61,17.2,4.78,1.29,.72,0];
plot(x,y); grid on;

semilogx(x,y); xlabel('Particle Size (mm)'); ylabel('Percent Passing (%)');

y60=60; 
xi=interp1(y,x,y60); hold on 
semilogy(xi,y60,'*r');

y30=30; xi=interp1(y,x,y30); hold on 
semilogy(xi,y30,'*r');

y10=10; xi=interp1(y,x,y10); hold on 
semilogy(xi,y10,'*r');

The code is fine......just flush the_semilogy_ next to hold on to next line.