How to Form Continuous Curve Plot

I have the following code. At the end, I issue the plot command. The resulting figure shows hundreds of discrete points along the plot. Is there someway to tell Matlab to connect those points to form a continuous curve, simply so the end product looks more like a curve instead of many tiny little dots?

I'm new, so please provide answers in simple terms with clear explanation, since I'm trying to learn and get a better understanding.

Thanks,

M Ridzon

%Define ratio of specific heats
gamma=1.4;

%Define gas constant
R=287;   %(J/Kg/K)

%Define reservoir properties
P_Res=500;   %(kPa)
T_Res=500;   %(Kelvin)

%Define nozzle exit area
NozArea=50;  %(cm^2)

%Find pressure ratio when nozzle exit plane becomes choked.
P_Ch=((1+((gamma-1)./2).*((1.0).^2)).^(gamma./(gamma-1))).^-1;

%From critical pressure ratio, find actual back pressure which causes choke
P_Crit=P_Res.*P_Ch;    %(kPa)

%Find density of fluid in reservoir
rho_Res=P_Res.*1000./R./T_Res;

%***********************************
%Calculate m-dot for choked case
%***********************************
%Find temperature of air exiting nozzle
T_Exit_Ch=T_Res./(1+((gamma-1)./2).*((1.0).^2));     %(K)

%Find speed of sound for the given temperature
a_Exit_Ch=(gamma.*R.*T_Exit_Ch).^0.5;        %(m/s)

%Find fluid density from equation of state
rho_Exit_Ch=(P_Crit.*10.^3)./R./T_Exit_Ch;        %(kg/m^3)

%Find m-dot
m_dot_Ch=rho_Exit_Ch*a_Exit_Ch*NozArea*((1/100)^2);   %(kg/s)

%***********************************
%Begin FOR loop
%***********************************
for i=0:P_Res/500:P_Res
    if i<=P_Crit
        m_dot=m_dot_Ch;
    else
        %Find mach speed of fluid exiting nozzle
        M=((2./(gamma-1)).*((P_Res./i).^((gamma-1)./gamma)-1)).^0.5;

          %Find temperature of air exiting nozzle
          T_Exit_Norm=T_Res./(1+((gamma-1)./2).*(M.^2));     %(K)

          %Find density of air exiting nozzle
          rho_Exit_Norm=rho_Res./((1+((gamma-1)./2).*(M.^2)).^(1./(gamma-1)));     %(kg/m^3)

          %Find speed of sound for the given temperature
          a_Exit_Norm=(gamma.*R.*T_Exit_Norm).^0.5;        %(m/s)

          %Find exit velocity
          V_Exit_Norm=M.*a_Exit_Norm;    %(m/s)

          %Find m-dot
          m_dot=rho_Exit_Norm*V_Exit_Norm*NozArea*((1/100)^2);   %(kg/s)
      end

      P_Ratio=i./P_Res;
      plot(P_Ratio,m_dot,'Color','k');
      hold on   %Hold plotting until the conclusion
  end

title('Ratio of Back Pressure to Reservoir Pressure vs. Mach Number')
xlabel('Pb / Pr')
ylabel('Mach Number')
hold off

Answer 1

[Star Strider]

Create ‘i’ as a vector, and then subscript it and your variables where necessary:

%***********************************
%Begin FOR loop
%***********************************
i=0:P_Res/5000:P_Res;
for k1 = 1:length(i)
    if i(k1)<=P_Crit
        m_dot(k1)=m_dot_Ch;
    else
        %Find mach speed of fluid exiting nozzle
        M=((2./(gamma-1)).*((P_Res./i(k1)).^((gamma-1)./gamma)-1)).^0.5;

          %Find temperature of air exiting nozzle
          T_Exit_Norm=T_Res./(1+((gamma-1)./2).*(M.^2));     %(K)

          %Find density of air exiting nozzle
          rho_Exit_Norm=rho_Res./((1+((gamma-1)./2).*(M.^2)).^(1./(gamma-1)));     %(kg/m^3)

          %Find speed of sound for the given temperature
          a_Exit_Norm=(gamma.*R.*T_Exit_Norm).^0.5;        %(m/s)

          %Find exit velocity
          V_Exit_Norm=M.*a_Exit_Norm;    %(m/s)

          %Find m-dot
          m_dot(k1)=rho_Exit_Norm*V_Exit_Norm*NozArea*((1/100)^2);   %(kg/s)
      end

      P_Ratio(k1)=i(k1)./P_Res;

end

plot(P_Ratio,m_dot,'Color','k');
hold on   %Hold plotting until the conclusion
title('Ratio of Back Pressure to Reservoir Pressure vs. Mach Number')
xlabel('Pb / Pr')
ylabel('Mach Number')
hold off

Every instance of ‘i’ in your original code should now be ‘i(k1)’. Check this in the event I missed any.

Also, it’s best not to use ‘i’ or ‘j’ as variables, including loop counters, because MATLAB uses them as its imaginary operators. Using them otherwise causes confusion.

Answer 2

[Matthew]

Star Strider,

Perfect! Got it! Thanks!

M Ridzon

[Star Strider]

My pleasure!