Using the piecewise function and integration function with fplot

How do I graph the three integral functions (V1,V2, &V3) below? I want to set the plot range for each of the three functions

%set up capacitor graph
V1 = (1/0.3e-9)*int(t*(5000/3),t); %Plot 0<t<3

Unrecognized function or variable 't'.

V2 = (1/0.3e-9)*int(5e-3,t); %Plot 3<t<6
V3 = (1/0.3e-9)*int(-5000*t+35e-3,t); %Plot 6<t<7
cap_volt = [V1 V2 V3];
fplot(cap_volt,[0 7])
%fplot(capacitor_voltage_values,[0 7]) %fplot defaults to [-5 5] so need to change range
%xlim([0 7]) %set the x-axis to 7
%ylim([-80 30])
title('capacitor voltage')
subtitle('V_L(t = 6.5\mus) = -75V')
xlabel('time (\mus)') %\mu adds the micro symbol to the x-axis label
ylabel('voltage (V)')
grid on

Answer 1

[Walter Roberson]

syms t
%set up capacitor graph
V1 = (1/0.3e-9)*int(t*(5000/3),t); %Plot 0<t<3
V2 = (1/0.3e-9)*int(5e-3,t); %Plot 3<t<6
V3 = (1/0.3e-9)*int(-5000*t+35e-3,t); %Plot 6<t<7
cap_volt = [V1 V2 V3];
fplot(cap_volt,[0 7])
%fplot(capacitor_voltage_values,[0 7]) %fplot defaults to [-5 5] so need to change range
%xlim([0 7]) %set the x-axis to 7
%ylim([-80 30])
title('capacitor voltage')
subtitle('V_L(t = 6.5\mus) = -75V')
xlabel('time (\mus)') %\mu adds the micro symbol to the x-axis label
ylabel('voltage (V)')
grid on

[madhan ravi]

Looks like the OP forgot to copy paste the syms t. As the plot produced by your code is already posted by the OP.

Answer 2

[Voss]

syms t
%set up capacitor graph
V1 = (1/0.3e-9)*int(t*(5000/3),t); %Plot 0<t<3
V2 = (1/0.3e-9)*int(5e-3,t); %Plot 3<t<6
V3 = (1/0.3e-9)*int(-5000*t+35e-3,t); %Plot 6<t<7
cap_volt = piecewise(0<t & t<3, V1, 3<t & t<6, V2, 6<t & t<7, V3);
fplot(cap_volt,[0 7])
%fplot(capacitor_voltage_values,[0 7]) %fplot defaults to [-5 5] so need to change range
%xlim([0 7]) %set the x-axis to 7
%ylim([-80 30])
title('capacitor voltage')
subtitle('V_L(t = 6.5\mus) = -75V')
xlabel('time (\mus)') %\mu adds the micro symbol to the x-axis label
ylabel('voltage (V)')
grid on

[Torsten]

Better define cap_volt also for t=0, t=3, t=6 and t=7.

[Voss]

I agree, but I'm doing what OP said he wanted.