Stopping a loop at the maximum value of y and finding the x from the maximum y

Hi everyone,

How can i stop the loop when i get the maximum M(i) and how do i know what is the value of the x (phi) for the maximum value of M?

Thank You.

b=300;  %mm
d=400;  %mm
fc=40;  %Mpa
Ecm=22*(fc/10)^0.3*10^3;  %Mpa
Es=200000;  %Mpa
As=2400;  %mm^2
fy=400;  %Mpa
epsc1=min(2.8/1000,0.7*fc^0.31/1000);
epscu=3.5/1000;
k=1.05*Ecm*epsc1/fc;

epscmv = linspace(0.05, 3.5, 50)*1E-3;
for i=1:50(epscmv);
    epscm = epscmv(i);
    funC=@(epsc) (k*epsc/epsc1-(epsc/epsc1).^2)./(1+(k-2)*epsc/epsc1);
    compression=@(c) b*fc*c/epscm*integral(funC,0,epscm)/1000;
    tension=@(c) min(Es*(d-c)/c*epscm*As/1000,fy*As/1000);
    c(i)=fsolve(@(c) compression(c)-tension(c),1);
    funM=@(epsc)(k*epsc./epsc1-(epsc./epsc1).^2)./(1+(k-2)*epsc./epsc1).*(d-c(i)+(c(i)./epscm).*epsc); 
    M(i)=b*fc*c(i)/epscm*integral(funM,0,epscm)/1000000;
    phi(i)=epscm/c(i);
end
Mmax=max(M(i))


plot(phi, M)
grid on
xlabel('phi  [1/mm]')
ylabel('Moment  [kNm]')

Answer 1

[David Hill]

b=300;  %mm
d=400;  %mm
fc=40;  %Mpa
Ecm=22*(fc/10)^0.3*10^3;  %Mpa
Es=200000;  %Mpa
As=2400;  %mm^2
fy=400;  %Mpa
epsc1=min(2.8/1000,0.7*fc^0.31/1000);
epscu=3.5/1000;
k=1.05*Ecm*epsc1/fc;
epscmv = linspace(0.05, 3.5, 50)*1E-3;
for i=1:50(epscmv);
    epscm = epscmv(i);
    funC=@(epsc) (k*epsc/epsc1-(epsc/epsc1).^2)./(1+(k-2)*epsc/epsc1);
    compression=@(c) b*fc*c/epscm*integral(funC,0,epscm)/1000;
    tension=@(c) min(Es*(d-c)/c*epscm*As/1000,fy*As/1000);
    c(i)=fsolve(@(c) compression(c)-tension(c),1);
    funM=@(epsc)(k*epsc./epsc1-(epsc./epsc1).^2)./(1+(k-2)*epsc./epsc1).*(d-c(i)+(c(i)./epscm).*epsc); 
    M(i)=b*fc*c(i)/epscm*integral(funM,0,epscm)/1000000;
    phi(i)=epscm/c(i);
end
[Mmax,idx]=max(M);%this is how you would get the max of M and the index at the maximum
phiAtmax=phi(idx);%using the index at maximum you can get the phi at the maximum
plot(phi, M)
grid on
xlabel('phi  [1/mm]')
ylabel('Moment  [kNm]')

[Shimon Katzman]

Thank you very much David.

Do you know how can i stop the loop when it gets to the maximum value of M?

[David Hill]

If your function is smooth and has only one peak, then you can just check when the value is less than the previous value and break.

for i=1:50(epscmv);
    epscm = epscmv(i);
    funC=@(epsc) (k*epsc/epsc1-(epsc/epsc1).^2)./(1+(k-2)*epsc/epsc1);
    compression=@(c) b*fc*c/epscm*integral(funC,0,epscm)/1000;
    tension=@(c) min(Es*(d-c)/c*epscm*As/1000,fy*As/1000);
    c(i)=fsolve(@(c) compression(c)-tension(c),1);
    funM=@(epsc)(k*epsc./epsc1-(epsc./epsc1).^2)./(1+(k-2)*epsc./epsc1).*(d-c(i)+(c(i)./epscm).*epsc); 
    M(i)=b*fc*c(i)/epscm*integral(funM,0,epscm)/1000000;
    phi(i)=epscm/c(i);
    if M(i)<M(i-1)
        break;
    end
end

[Shimon Katzman]

doesnt work

Attempted to access M(0); index must be a positive integer or logical.

Error in advencedconcrete32a (line 22)
    if M(i)<M(i-1)