Real analysis is not entirely non-constructive… better? Double/triple negatives are not uncommon in proof writing…
Yes. Measure theory in particular is by and large very non-constructive. You in fact were who made an even broader claim: “Most real analysis is non-constructive...”
Fair enough. I'll post soon a nice example of an ordinary differential equation (ODE) from Rudin (1964) himself;
page 102, exercis 17
page 156, exercise 22.
The exercises are incomplete as he is essentially trying to jam ODE into 2 exercises, something 1st/2nd year undergrad will not grasp. In my ODE/PDE course for US students (e.g. UCB), we devote a full module (module A) to ODE, taken from multiple perspectives.
You in fact were who made an even broader claim: “Most real analysis is non-constructive...”
Generallly, most pure maths is concerned with existence and uniqueness proofs. In contrast, see Bishop.
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Many of the pure mathematicians I knew were focused on one approach to solving problems. I like Polya's approach
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“It is better to solve one problem five different ways, than to solve five problems one way.”
― George Pólya
e.g. for ODE we have
analytical solution (most students seem to learn ODE in this way only, grosso modo??)
Picard iteration
Finite difference
Transformation (variables separable)