# How to mark points at 1-5 on the x-axis in the plot

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Aijalon Marsh on 13 Oct 2023
Edited: Star Strider on 13 Oct 2023
clc;
clear all ;
Ld=(0:0.00005:0.005);
w=0.001;
L=0.007;
P=4*0.001;
Ta=25;
h=375;
Kf=175;
Kd=0.032;
Tb=75;
Ap=3.02*10^-3;
N=238;
Ac=10^-6;
m=92.6;
Lf=L-Ld;
Rtf=(cosh(m.*Lf)+(h./(m.*Kf)).*sinh(m.*Lf))./(sqrt(4*h.*(w)^3*Kf).*(sinh(m.*Lf)+h./(m.*Kf)).*cosh(m.*Lf));
R_fins=Rtf/N;
Rf_cond=Ld/(Kf*N*Ac);
Rd_cond=Ld/(Kd*(Ap-N*Ac));
q=(Tb-Ta)./(Rd_cond+R_conv)+(Tb-Ta)./(Rf_cond+R_fins);
Q=min(q);
figure
plot(Ld, q);
xlabel('Dust layer thickness, Ld (m)');
ylabel('Heat Rate, q(W)');
grid on;
fprintf("Total heat rate %.2f°C\n", Q);
Dyuman Joshi on 13 Oct 2023
Edited: Dyuman Joshi on 13 Oct 2023
What do you mean by "mark points at 1-5 on the x-axis in the plot"?
Could you give an example of what the expected output is?
Aijalon Marsh on 13 Oct 2023
should look like that.

Star Strider on 13 Oct 2023
Edited: Star Strider on 13 Oct 2023
One possibility —
clc;
clear all ;
Ld=(0:0.00005:0.005);
w=0.001;
L=0.007;
P=4*0.001;
Ta=25;
h=375;
Kf=175;
Kd=0.032;
Tb=75;
Ap=3.02*10^-3;
N=238;
Ac=10^-6;
m=92.6;
Lf=L-Ld;
Rtf=(cosh(m.*Lf)+(h./(m.*Kf)).*sinh(m.*Lf))./(sqrt(4*h.*(w)^3*Kf).*(sinh(m.*Lf)+h./(m.*Kf)).*cosh(m.*Lf));
R_fins=Rtf/N;
Rf_cond=Ld/(Kf*N*Ac);
Rd_cond=Ld/(Kd*(Ap-N*Ac));
q=(Tb-Ta)./(Rd_cond+R_conv)+(Tb-Ta)./(Rf_cond+R_fins);
Q=min(q);
figure
plot(Ld, q);
xlabel('Dust layer thickness, Ld (m)');
ylabel('Heat Rate, q(W)');
grid on;
fprintf("Total heat rate %.2f°C\n", Q);
Total heat rate 37.54°C
xlim([0 6]*1E-3)
Ldq = get(gca,'XTick');
qv = interp1(Ld, q, Ldq);
idx = isfinite(qv);
text(Ldq(idx), qv(idx), compose('Ld = %.3f\nq = %8.3f\n\\downarrow',[Ldq(idx); qv(idx)]'), 'Horiz','left', 'Vert','bottom', 'FontSize',8)
.

Dyuman Joshi on 13 Oct 2023
Edited: Dyuman Joshi on 13 Oct 2023
Okay, you want to create data-tips. Data-tips can be added using datatip -
Ld=(0:0.00005:0.005);
w=0.001;
L=0.007;
P=4*0.001;
Ta=25;
h=375;
Kf=175;
Kd=0.032;
Tb=75;
Ap=3.02*10^-3;
N=238;
Ac=10^-6;
m=92.6;
Lf=L-Ld;
Rtf=(cosh(m.*Lf)+(h./(m.*Kf)).*sinh(m.*Lf))./(sqrt(4*h.*(w)^3*Kf).*(sinh(m.*Lf)+h./(m.*Kf)).*cosh(m.*Lf));
R_fins=Rtf/N;
Rf_cond=Ld/(Kf*N*Ac);
Rd_cond=Ld/(Kd*(Ap-N*Ac));
q=(Tb-Ta)./(Rd_cond+R_conv)+(Tb-Ta)./(Rf_cond+R_fins);
Q=min(q);
figure
p = plot(Ld, q);
xlabel('Dust layer thickness, Ld (m)');
ylabel('Heat Rate, q(W)');
grid on;
fprintf("Total heat rate %.2f°C\n", Q);
Since only 1 data-tip can be added at a time, use a for loop -
%Define the x values to get data-tips for
vec = (1:5)/1e3;
for k=vec
%% Using tolerance to compare floating point numbers
%The highest significant digit of values in Ld is 5, corresponding to
%10^-5 or 1e-5, thus select a tolerance smaller than that
idx = abs(Ld-k)<1e-6;
datatip(p, Ld(idx), q(idx))
end
As the graph is monotonic, there is only 1 y-point corresponding to a single x-point. Thus we can directly use logical-indexing.
For other cases, the code might need modifications.