This model assumes that the value of input current is constant. Therefore the inductor current and capacitor current are in antiphase.

ic = i_in - i_L

In real converter the input current isn't constant.

Thank you dear Lukasz, but why in order to get input current is constant, the inductor current and capacitor current must be in antiphase?

The Kirchhoff's first law says that:

"At any node (junction) in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node".

so then

i_in = i_c + i_L => i_c = i_in - i_L

i_in is constant, i_L is a triangular shaped waveform, conseqently i_c is also a triangular shaped waveform but in antiphase to inductor current.

Thank you !

As per your given waveforms and from basic working principle of boost converter. When Inductor is energizing, input capacitor is discharging and visa versa.so current rise and fall states of inductor and capacitor are antiparallel.