app.py

import streamlit as st
import numpy as np
import plotly.graph_objs as go
import sympy as sp

st.set_page_config(page_title="Gradient Descent Visualizer", layout="wide")

st.markdown("""
    <style>
    html, body, [class*="css"] {
        font-family: 'Segoe UI', sans-serif;
        background-color: #ffffff;
        color: #222;
    }
    h1 {
        font-size: 36px;
        font-weight: 700;
        margin-bottom: 0.5em;
    }
    .stTextInput > div > input {
        border: 2px solid #00d0b6;
        border-radius: 8px;
        padding: 0.5em;
        font-size: 16px;
    }
    .stButton > button {
        background-color: #00d0b6;
        color: white;
        font-weight: 600;
        border-radius: 8px;
        padding: 0.6em 1.2em;
        font-size: 16px;
    }
    .stButton > button:hover {
        background-color: #00baa5;
        transition: 0.3s;
    }
    .stMarkdown {
        font-size: 18px;
        font-weight: 500;
    }
    .element-container:has(.stButton) {
        margin-top: 1em;
        margin-bottom: 1em;
    }
    .stColumns {
        gap: 0.5rem !important;
    }
    .st-c1 {
        font-weight: bold;
    }
    .stSuccess {
        font-size: 18px;
        font-weight: 600;
        color: white;
        background-color: #00d0b6;
        border-radius: 6px;
        padding: 0.4em 0.8em;
    }
    </style>
""", unsafe_allow_html=True)

st.title("Interactive Gradient Descent Visualizer")

x = sp.Symbol('x')

defaults = {
    "step": 0,
    "points": [],
    "gradient_func": None,
    "func": None,
    "parsed_func": None,
    "func_input": "x^2+x"
}

for key, val in defaults.items():
    if key not in st.session_state:
        st.session_state[key] = val

st.session_state.func_input = st.text_input("Function", st.session_state.func_input)

st.markdown("Try these functions:")
c1, c2, c3, c4, c5 = st.columns(5)
if c1.button("x²"):
    st.session_state.func_input = "x^2"
if c2.button("x³"):
    st.session_state.func_input = "x^3"
if c3.button("sin(x)"):
    st.session_state.func_input = "sin(x)"
if c4.button("1/x"):
    st.session_state.func_input = "1/x"
if c5.button("Polynomial"):
    st.session_state.func_input = "x**4 - 3*x**3 + 2"

start_point = st.text_input("Starting Point", "5")
setup = st.button("Set Up")

if setup:
    try:
        st.session_state.step = 0
        st.session_state.points = []
        expr = st.session_state.func_input.replace("^", "**")
        parsed = sp.sympify(expr)
        st.session_state.parsed_func = parsed
        st.session_state.func = sp.lambdify(x, parsed, "numpy")
        grad = sp.diff(parsed, x)
        st.session_state.gradient_func = sp.lambdify(x, grad, "numpy")
        st.session_state.points.append(float(start_point))
    except Exception as e:
        st.error(f"Error parsing function: {e}")

learning_rate = st.text_input("Learning Rate", "0.01")

if st.button("Next Iteration"):
    if st.session_state.func is None or st.session_state.gradient_func is None or len(st.session_state.points) == 0:
        st.warning("Please set up the function first.")
    else:
        try:
            lr = float(learning_rate)
            x_curr = st.session_state.points[-1]
            grad_val = st.session_state.gradient_func(x_curr)
            x_next = x_curr - lr * grad_val
            st.session_state.points.append(x_next)
            st.session_state.step += 1
        except Exception as e:
            st.error(f"Iteration error: {e}")

if st.session_state.func is not None and len(st.session_state.points) > 0:
    try:
        min_x = min(min(st.session_state.points), -6)
        max_x = max(max(st.session_state.points), 6)
        margin = (max_x - min_x) * 0.2 if max_x > min_x else 1
        x_vals = np.linspace(min_x - margin, max_x + margin, 400)

        y_vals = st.session_state.func(x_vals)
        iter_points = np.array(st.session_state.points)
        iter_y = st.session_state.func(iter_points)

        trace1 = go.Scatter(x=x_vals, y=y_vals, mode='lines', name='Function', line=dict(color='blue'))
        trace2 = go.Scatter(x=iter_points, y=iter_y, mode='markers+lines', name='Gradient Descent Path', marker=dict(color='red'))
        trace3 = go.Scatter(x=[iter_points[-1]], y=[iter_y[-1]], mode='markers+text',
                            marker=dict(color='green', size=12),
                            text=[f"{iter_points[-1]:.6f}"],
                            textposition="top center",
                            name="Current Point")

        layout = go.Layout(title=f"Iteration {st.session_state.step}",
                           xaxis=dict(title="x - axis"),
                           yaxis=dict(title="y - axis"))

        fig = go.Figure(data=[trace1, trace2, trace3], layout=layout)
        st.plotly_chart(fig, use_container_width=True)
        st.success(f"Current Point = {iter_points[-1]}")
    except Exception as e:
        st.error(f"Plot error: {e}")