Mat Date Picker set Default value, Previous Sunday and Saturday

https://stackblitz.com/edit/ng-mat-date-value-binding-kk-12?embed=1&file=app/datepicker-value-example.html&view=preview

<mat-form-field>
  <input matInput [matDatepicker]="picker3" placeholder="Value binding" [value]="startDate.value">
  <mat-datepicker-toggle matSuffix [for]="picker3"></mat-datepicker-toggle>
  <mat-datepicker #picker3></mat-datepicker>
</mat-form-field>
<mat-form-field>
  <input matInput [matDatepicker]="picker4" placeholder="Value binding" [value]="endDate.value">
  <mat-datepicker-toggle matSuffix [for]="picker4"></mat-datepicker-toggle>
  <mat-datepicker #picker4></mat-datepicker>
</mat-form-field>

import { Component } from "@angular/core";
import { FormControl } from "@angular/forms";
/** @title Datepicker selected value */
@Component({
  selector: "datepicker-value-example",
  templateUrl: "datepicker-value-example.html",
  styleUrls: ["datepicker-value-example.css"]
})
export class DatepickerValueExample {
  today = new Date();
  sunday = new Date(
    this.today.getFullYear(),
    this.today.getMonth(),
    this.today.getDate() - this.today.getDay()
  );
  prevSunday = new Date(
    new Date(this.sunday).setDate(this.sunday.getDate() - 7)
  );
  prevSaturday = new Date(
    new Date(this.prevSunday).setDate(this.prevSunday.getDate() + 6)
  );
  startDate: any = new FormControl(this.prevSunday.toISOString());
  endDate: any = new FormControl(this.prevSaturday.toISOString());
}