how to solve this

p=[101.3 106.6 109.4 114.7 116.9 118.2 123.7]; 
v=[1.69 3.67 4.37 5.45 5.84 6.05 6.90]; 
% 4 ways for interpolation
lin=interp1(v,p,5,'linear') 
m=interp1(v,p,5,'makima') 
sp=interp1(v,p,5,'spline') 
n=interp1(v,p,5,'nearest')

% Display a graph of speed versus pressure, the graph will include the given measurements

as well as the results obtained using 4 methods interpolation.

Mark with a red asterisk the points where the speed is 5 [m/s.]

* Labels must be added to the axes, legend, grid lines and title.

Answer 1

[Image Analyst]

You almost got it. Maybe you just needed to read the manual some more and understand what is x and what is y.

p=[101.3 106.6 109.4 114.7 116.9 118.2 123.7]; 
v=[1.69 3.67 4.37 5.45 5.84 6.05 6.90]; 
plot(p, v, 'b.-', 'LineWidth', 2, 'MarkerSize', 20);
grid on;
xlabel('Pressure');
ylabel('Velocity');
% 4 ways for interpolation
xq = linspace(min(p), max(p), 500);
lin=interp1(p, v, xq,'linear') ;
m=interp1(p, v, xq,'makima'); 
sp=interp1(p, v, xq,'spline') ;
n=interp1(p, v, xq,'nearest');
% Find where speed is closest to 5
[value, index] = min(abs(lin - 5)) % Value is how far away from 5 the data point is.

value = 0.0029

index = 250

x5 = xq(index)

x5 = 112.4776

y5 = lin(index)

y5 = 4.9971

hold on;
yline(5, 'Color', 'r') % Horizontal red line at 5.
xline(x5, 'Color', 'r') % Horizontal red line at 5.
% Plot a red asterisk at the point closest to y=5
plot(x5, y5, 'r*', 'MarkerSize', 30, 'LineWidth', 2)

Go ahead and add the rest, like legend, title, etc.

[daniel]

tnks!

Answer 2

[Walter Roberson]

When you call plot, you can use

plot(x1, y1, x2, y2, x3, y3, ...)

where x1 and x2 and x3 and so on might happen to all be the same.

You can label using xlabel ylabel legend grid

For the part about red: see https://www.mathworks.com/help/matlab/creating_plots/create-line-plot-with-markers.html#bvcbmlx-1

[daniel]

you can show me ? i try....

[daniel]

plot(v,p,lin,m,sp,n,'r*',5)
legend('pressure','velocity')
ylabel('pressure [kpa]')
xlabel('velocity m/s')
hold off
title('pressure by velocity')

[daniel]

but this is not interpolation

[Walter Roberson]

plot(v,p,lin,m,sp,n,'r*',5)

That code asks to use v as the first independent variable, and plot p as dependent on it. And then to take lin as the next independent variable and plot m as depedent on it.

Contrast to

plot(v, p, v, lin, v, ...)