MATLAB: Displaying values in command window

displayplot

hi, trying to display some values but am not sure how to go about it, this is a pH array, Vb is volume of base added. What i am trying to do is display the midpoint to equivalence which is the half of Vb_ev and then display the corresponding pH value at midpoint, which i know is approx 4.756. see on from line 6 from the bottom.
      format short
      Kw = 1e-14;
      Ka = 1.755388e-5;
      pKa = 4.756;
      %
      Ca = 0.5;
      Cb = 0.1;
      Va = 100;
      Vb = 0.05:0.05:2000;
      Ma = (Ca * Va) / 1000;
      Mb = (Cb .* Vb) ./ 1000;
      for i = 1:length(Mb)
        M_excess = Ma - Mb(i);
        if abs(M_excess)<eps
            Hplus = Ka * ((Ma_final * 0.999999) ./ Mb_final);
            Vb_ev = Vb(i); 
            pH_ev = pH(end); 
        elseif M_excess > 0
            Ma_final = (M_excess * 1000) ./ (Va + Vb(i));
            Mb_final = (Mb(i) * 1000) ./ (Va + Vb(i));
            Hplus = Ka * (Ma_final ./ Mb_final);
        elseif M_excess < 0
            OH = (M_excess * 1000 * (-1)) ./ (Va + Vb(i));
            Hplus = Kw ./ OH;
        end
        pH(i) = -log10(Hplus);
      end
      % 
      Vb_Mid_Pt1 = (Vb_ev)*0.5;
      pH_Mid_Pt1 = i want to display pH at Vb_Mid_Pt1;
      disp('The Volume is, mL:')
      disp(Vb_Mid_Pt1)
      disp('The pH is:')
      disp(pH_Mid_Pt1)

Best Answer

the reason you are getting such error is the index Vb_Mid_Pt1 is not integer. if u cast that it works fine. here you go
format short
      Kw = 1e-14;
      Ka = 1.755388e-5;
      pKa = 4.756;
      %
      Ca = 0.5;
      Cb = 0.1;
      Va = 100;
      Vb = 0.05:0.05:2000;
      Ma = (Ca * Va) / 1000;
      Mb = (Cb .* Vb) ./ 1000;
      for i = 1:length(Mb)
        M_excess = Ma - Mb(i);
        if abs(M_excess)<eps
            Hplus = Ka * ((Ma_final * 0.999999) ./ Mb_final);
            Vb_ev = Vb(i); 
            pH_ev = pH(end); 
        elseif M_excess > 0
            Ma_final = (M_excess * 1000) ./ (Va + Vb(i));
            Mb_final = (Mb(i) * 1000) ./ (Va + Vb(i));
            Hplus = Ka * (Ma_final ./ Mb_final);
        elseif M_excess < 0
            OH = (M_excess * 1000 * (-1)) ./ (Va + Vb(i));
            Hplus = Kw ./ OH;
        end
        pH(i) = -log10(Hplus);
      end
      % 
      Vb_Mid_Pt1 = uint16(Vb_ev)*0.5;
      pH_Mid_Pt1 = pH(Vb_Mid_Pt1);%i want to display pH at Vb_Mid_Pt1;
      disp('The Volume is, mL:')
      disp(Vb_Mid_Pt1)
      disp('The pH is:')
      disp(pH_Mid_Pt1)
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