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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def modify_qa_v1(self):
 """Add water to or remove water from the calculated lake outflow. Required control parameter: |Verzw| Required derived parameter: |llake_derived.TOY| Updated flux sequence: |llake_fluxes.QA| Basic Equation: :math:`QA = QA* - Verzw` Examples: In preparation for the following examples, define a short simulation time period with a simulation step size of 12 hours and initialize the required model object: Select the first half of the second day of January as the simulation step relevant for the following examples: Assume that, in accordance with previous calculations, the original outflow value is 3 m³/s: Prepare the shape of parameter `verzw` (usually, this is done automatically when calling parameter `n`):
 Set the value of the abstraction on the first half of the second day of January to 2 m³/s: In the first example `verzw` is simply subtracted from `qa`: qa(1.0) In the second example `verzw` exceeds `qa`, resulting in a zero outflow value: qa(0.0) The last example demonstrates, that "negative abstractions" are allowed, resulting in an increase in simulated outflow: qa(2.0) """


    con = self.parameters.control.fastaccess
    der = self.parameters.derived.fastaccess
    flu = self.sequences.fluxes.fastaccess
    idx = der.toy[self.idx_sim]
    flu.qa = max(flu.qa-con.verzw[idx], 0.)