# Codercise PF4.5b - Requested array has an inhomogeneous shape after 1 dimension

**URL:** <https://discuss.pennylane.ai/t/codercise-pf4-5b-requested-array-has-an-inhomogeneous-shape-after-1-dimension/8251>\
**Category:** Codebook\
**Created:** [March 18, 2025, 7:32pm UTC](https://discuss.pennylane.ai/t/codercise-pf4-5b-requested-array-has-an-inhomogeneous-shape-after-1-dimension/8251 "2025-03-18T19:32:36Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![mack.attack](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/mack.attack/32/2772_2.png) [@mack.attack](https://discuss.pennylane.ai/u/mack.attack)\
**Post date:** [March 18, 2025, 7:32pm UTC](https://discuss.pennylane.ai/t/codercise-pf4-5b-requested-array-has-an-inhomogeneous-shape-after-1-dimension/8251/1 "2025-03-18T19:32:36Z")

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G’day, this is Mack again, starting a new project with PennyLane and revamping the quanvolutional neural network before this summer.

Being a followup of PF4.5a, I am now stuck on PF4.5b where I have to implement the actual machine learning part (gradient descent).

The code for PF4.5a is based on the corresponding _related theory_, where the `opt.step(cost_function, params)` are repeatedly ran.

The circuit from PF4.5a consists of four elements. Thus, there are four elements in the `init_params`. However, whenever I attempt to run the code using a four-element `init_params`, the output errors out with

> Error: setting an array element with a sequence. The requested array has an inhomogeneous shape after 1 dimensions. The detected shape was (2,) + inhomogeneous part.

Even then, after adding the print function to see the results, I can see that the optimization is still working. This is my code so far:

```auto
def optimize(cost_function, init_params, steps):

    opt = qml.GradientDescentOptimizer(stepsize = 0.2) # Change this as you see fit

    params = init_params

    for i in range(steps):
        print(params)
        params = opt.step(cost_function, params)

    return params, cost_function(params)

minimum = optimize(cost_function, np.array([0.7,0.3,0.2,0.5], requires_grad = True), 1) # An np.tensor of shape () containing the minimum of cost_function.

```

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<div class="post-metadata">

**Author:** ![mack.attack](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/mack.attack/32/2772_2.png) [@mack.attack](https://discuss.pennylane.ai/u/mack.attack)\
**Post date:** [March 18, 2025, 7:36pm UTC](https://discuss.pennylane.ai/t/codercise-pf4-5b-requested-array-has-an-inhomogeneous-shape-after-1-dimension/8251/2 "2025-03-18T19:36:14Z")

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Hint: You are really outputting two pieces, namely the params and the cost function given params after optimization. You need to index the output!

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**Author:** ![daniela.murcillo](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/daniela.murcillo/32/3612_2.png) [@daniela.murcillo](https://discuss.pennylane.ai/u/daniela.murcillo)\
**Post date:** [March 19, 2025, 1:59pm UTC](https://discuss.pennylane.ai/t/codercise-pf4-5b-requested-array-has-an-inhomogeneous-shape-after-1-dimension/8251/3 "2025-03-19T13:59:23Z")

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Hi @mack.attack !  
Thanks for your question.  
You are on the right track, quite close to the solution! There are two things that I would recommend:

1. Use the hint and select the part of the output that contains the minimum value. The output is a tuple with two objects, take the second one. `minimum = optimize(cost_function, np.array([0.7,0.3,0.2,0.5], requires_grad = True), 1)[1]`
2. Remember that this is an optimization and you need several steps in order to get a minimum value within certain tolerance. Our evaluation code is checking if your minimum value is close enough to the answer within certain tolerance. Try increasing the number of steps; currently, your program is only doing one.

Let us know if this helped!

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<div class="post-metadata">

**Author:** ![mack.attack](https://yyz2.discourse-cdn.com/flex012/user_avatar/discuss.pennylane.ai/mack.attack/32/2772_2.png) [@mack.attack](https://discuss.pennylane.ai/u/mack.attack)\
**Post date:** [March 26, 2025, 4:07am UTC](https://discuss.pennylane.ai/t/codercise-pf4-5b-requested-array-has-an-inhomogeneous-shape-after-1-dimension/8251/4 "2025-03-26T04:07:15Z")

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I am able to figure this shortly after reading the question more closely, what they are precisely looking for.